Editing Latin declension (section)

== Nouns ==
There are two principal parts for Latin nouns: the nominative singular and the genitive singular. Each declension can be unequivocally identified by the ending of the genitive singular (-''ae'', -''i'', -''is'', -''ūs'', -''ei''). The stem of the noun can be identified by the form of the genitive singular as well.

There are five declensions for Latin nouns:

=== {{anchor|d1}}{{anchor|First declension}} First declension (''a'' stems) ===
Nouns of this declension usually end in ''-a'' in the nominative singular and are mostly feminine, e.g. {{wikt-lang|la|via|via, viae}} {{abbr|f.|feminine}} ('road') and {{wikt-lang|la|aqua|aqua, aquae}} {{abbr|f.|feminine}} ('water'). There is a small class of masculine exceptions generally referring to occupations, e.g. {{wikt-lang|la|poeta|poēta, poētae}} {{abbr|m.|masculine}} ('poet'), {{wikt-lang|la|agricola|agricola, agricolae}} {{abbr|m.|masculine}} ('farmer'), {{wikt-lang|la|auriga|auriga, aurigae}} {{abbr|m.|masculine}} ('auriga, charioteer'), {{wikt-lang|la|pirata|pīrāta, pīrātae}} {{abbr|m.|masculine}} ('pirate') and {{wikt-lang|la|nauta|nauta, nautae}} {{abbr|m.|masculine}} ('sailor').

The predominant letter in the ending forms of this declension is ''a''. The nominative singular form consists of the [[stem (linguistics)|stem]] and the [[Suffix#Inflectional suffixes|ending]] ''-a'', and the genitive singular form is the stem plus ''-ae''.

{| class="wikitable"
|+ First declension paradigm
|-
!
! Singular || Plural
|-
! Nominative, Vocative
| -a || -ae
|-
! Accusative
| -am || -ās
|-
! Genitive
| rowspan="2" |  -ae || -ārum
|-
! Dative
| rowspan="2" | -īs
|-
! Ablative
| -ā
|-
! Locative
| ''Gen.'' || ''Dat.''
|}
{| class="wikitable"
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|mensa|mensa, mensae}}<br />table {{abbr|(f.)|feminine}}
! colspan="2" | {{wikt-lang|la|poeta|poēta, poētae}}<br />poet {{abbr|(m.)|masculine}}
|-
! Singular
! Plural
! Singular
! Plural
|-
! Nominative, Vocative
| mensa || mensae || poēta || poētae
|-
! Accusative
| mensam || mensās || poētam || poētās
|-
! Genitive
| rowspan="2" | mensae{{efn-lr|The archaic genitive ending in ''-ai'' (as in ''aquai'') occurs occasionally in [[Virgil]] and [[Lucretius]], to evoke the style of older writers. Plus, the archaic genitive ending in -ās is used in expressions like ''pater familiās'' (also possible in conjunction with ''māter'', ''fīlius'' and ''fīlia'').}} || mensārum || rowspan="2" | poētae || poētārum
|-
! Dative
| rowspan="2" | mensīs || rowspan="2" | poētīs
|-
! Ablative
| mensā || poētā
|}
{{notelist-lr}}
The locative endings for the first declension are ''-ae'' (singular) and ''-īs'' (plural), similar to the genitive singular and ablative plural, as in ''{{wikt-lang|la|mīlitia|mīlitiae}}'' 'in war' and ''{{wikt-lang|la|Athēnae|Athēnīs}}'' 'at Athens'.<ref>Allen and Greenough. §43 c.</ref>

==== {{anchor|d1g}} First declension Greek nouns ====

{{Main|Declension of Greek nouns in Latin}}

The first declension also includes three types of [[Ancient Greek|Greek]] loanwords, derived from Ancient Greek's [[Ancient Greek nouns#First declension|alpha declension]]. They are declined irregularly in the singular, but sometimes treated as native Latin nouns, e.g. nominative {{wikt-lang|la|athleta|athlēt'''a'''}} ('athlete') instead of the original ''athlēt'''ēs'''''. Archaic ([[Homer]]ic) first declension Greek nouns and adjectives had been formed in exactly the same way as in Latin: ''nephelēgerét'''a''' Zeus'' ('[[Zeus]] the cloud-gatherer') had in classical Greek become ''nephelēgerét'''ēs'''''.

For full paradigm tables and more detailed information, see the Wiktionary appendix [[wiktionary:Appendix:Latin first declension|First declension]].

=== {{anchor|d2}}{{anchor|Second declension}} Second declension (''o'' stems) ===
The second declension is a large group of nouns consisting of mostly masculine nouns like {{wikt-lang|la|equus|equus, equī}} ('horse') and {{wikt-lang|la|puer|puer, puerī}} ('boy') and neuter nouns like {{wikt-lang|la|castellum|castellum, castellī}} ('fort'). There are several small groups of feminine exceptions, including names of [[gemstone]]s, plants, trees, and some towns and cities.

In the nominative singular, most masculine nouns consist of the [[Stem (linguistics)|stem]] and the [[Suffix#Inflectional suffixes|ending]] ''-us'', although some end in ''-er'', which is not necessarily attached to the complete stem. Neuter nouns generally have a nominative singular consisting of the stem and the ending ''-um''. However, every second-declension noun has the ending ''-ī'' attached as a suffix to the root of the noun in the genitive singular form. The predominant letter in the ending forms of this declension is ''o''.

{| class="wikitable"
|+ Second declension paradigm
|-
! rowspan="2" |
! colspan="2" | Singular
! colspan="2" | Plural
|-
! Masculine || Neuter
! Masculine || Neuter
|-
! Nominative
| -us  ||   rowspan="3"| -um || rowspan="2"| -ī ||rowspan="3"| -a
|-
! Vocative
| -e
|-
! Accusative
| -um || -ōs
|-
! Genitive
| colspan="2"|-ī ||colspan="2"| -ōrum
|-
! Dative, Ablative
| colspan="2" | -ō  || colspan="2" | -īs
|-
! Locative
| colspan="2"| ''Gen.'' || colspan="2"| ''Dat.''
|}
{| class="wikitable"
|+ Masculine
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|dominus|dominus, dominī}}<br />master {{abbr|m.|masculine}}
|-
! Singular
! Plural
|-
! Nominative
| dominus || rowspan="2" | dominī
|-
! Vocative
| domine
|-
! Accusative
| dominum || dominōs
|-
! Genitive
| dominī || dominōrum
|-
! Dative, Ablative
| dominō || dominīs
|}

{| class="wikitable"
|+ Neuter
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|bellum|bellum, bellī}}<br />war {{abbr|n.|neuter}}
|-
! Singular
! Plural
|-
! Nominative, Vocative, Accusative
| bellum || bella
|-
! Genitive
| rowspan="2" | bellī || bellōrum
|-
! Locative
| rowspan="2" | bellīs
|-
! Dative, Ablative
| bellō
|}

The locative endings for the second declension are ''-ī'' (singular) and ''-īs'' (plural); {{wikt-lang|la|Corinthus|Corinthī}} "at Corinth", {{wikt-lang|la|Mediolanum|Mediolānī}} "at Milan", and {{wikt-lang|la|Philippi|Philippīs}} "at Philippi".<ref>Allen and Greenough. §49 a.</ref>

==== {{anchor|d2r}} Second-declension ''-ius'' and ''-ium'' nouns ====
Nouns ending in ''-ius'' and ''-ium'' have a genitive singular in ''-ī'' in earlier Latin, which was regularized to ''-iī'' in the later language. Masculine nouns in ''-ius'' have a vocative singular in ''-ī'' at all stages. These forms in ''-ī'' are stressed on the same syllable as the nominative singular, sometimes in violation of the usual Latin stress rule. For example, the genitive and vocative singular ''Vergilī'' (from {{wikt-lang|la|Vergilius}}) is pronounced ''Vergílī'', with stress on the penult, even though it is short.<ref>Gildersleeve & Lodge §15, Allen & Greenough §12, §49c</ref> In Old Latin, however, the vocative was declined regularly, using ''-ie'' instead, e.g. ''fīlie'' "[O] son", archaic vocative of {{Lang|la|fīlius}}.

There is no contraction of ''-iī(s)'' in plural forms and in the locative.

{| class="wikitable"
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|filius|fīlius, filiī}}<br />son {{abbr|m.|masculine}}
! colspan="2" | {{wikt-lang|la|auxilium|auxilium, auxiliī}}<br />aid, help {{abbr|n.|neuter}}
|-
! Singular
! Plural
! Singular
! Plural
|-
! Nominative
| {{Lang|la|fīlius}} || rowspan="2" | {{Lang|la|fīliī}}  || rowspan="3" | {{Lang|la|auxilium}}  || rowspan="3" | {{Lang|la|auxilia}}
|-
! Vocative
| {{Lang|la|fīlī}}
|-
! Accusative
| {{Lang|la|fīlium}} || {{Lang|la|fīliōs}}
|-
! Genitive
| {{Lang|la|fīliī}}  || {{Lang|la|fīliōrum}}  || {{Lang|la|auxiliī}}  || {{Lang|la|auxiliōrum}}
|-
! Dative, Ablative
| {{Lang|la|fīliō}}  || {{Lang|la|fīliīs}}  || {{Lang|la|auxiliō}}  || {{Lang|la|auxiliīs}}
|}

In the older language, nouns ending with ''-vus'', ''-quus'' and ''-vum'' take ''o'' rather than ''u'' in the nominative and accusative singular. For example, {{wikt-lang|la|servis|servus, servī}} ('slave') could be ''servos'', accusative ''servom''.

==== {{anchor|d2r}} Second-declension ''-r'' nouns ====
Some masculine nouns of the second declension end in ''-er'' or ''-ir'' in the nominative singular. The declension of these nouns is identical to that of the regular second declension, except for the lack of suffix in the nominative and vocative singular.

Some (but not all) nouns in ''-er'' drop the ''e'' in the genitive and other cases. For example, {{wikt-lang|la|socer|socer, socerī}} ('father-in-law') keeps its ''e''. However, the noun {{wikt-lang|la|magister|magister, magistrī}} ('(school)master') drops its ''e'' in the genitive singular.

For declension tables of second-declension nouns, see the [[Wiktionary:Appendix:Latin second declension|corresponding Wiktionary appendix]].

{| class="wikitable"
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|puer|puer, puerī}}<br />boy {{abbr|m.|masculine}}
! colspan="2" | {{wikt-lang|la|ager|ager, agrī}}<br />field {{abbr|m.|masculine}}
! colspan="2" | {{wikt-lang|la|vir|vir, virī}}<br />man {{abbr|m.|masculine}}
|-
! Singular
! Plural
! Singular
! Plural
! Singular
! Plural
|-
! Nominative,Vocative
| puer || puerī || ager || agrī || vir || virī
|-
! Accusative
| puerum || puerōs || agrum || agrōs || virum || virōs
|-
! Genitive
| puerī || puerōrum || agrī || agrōrum || virī || virōrum<br />(virum)
|-
! Dative, Ablative
| puerō || puerīs || agrō || agrīs || virō || virīs
|}

The vocative ''puere'' is found but only in [[Plautus]].<ref>[https://www.perseus.tufts.edu/hopper/searchresults?target=la&all_words=puere Perseus database.]</ref> The genitive plural ''virum'' is found in poetry.<ref>Gildersleeve & Lodge, ''Latin Grammar'' 3rd ed., p. 17.</ref>

==== {{anchor|d2g}} Second-declension Greek nouns ====

{{Main|Declension of Greek nouns in Latin}}

The second declension contains two types of masculine Greek nouns and one form of neuter Greek noun. These nouns are irregular only in the singular, as are their first-declension counterparts. Greek nouns in the second declension are derived from the [[Ancient Greek nouns#Second declension|Omicron declension]].

Some Greek nouns may also be declined as normal Latin nouns. For example, {{wikt-lang|la|theātron}} can appear as ''theātrum''.

==== {{anchor|d2i}} Irregular forms ====

===== Deus =====
The inflection of {{wikt-lang|la|deus|deus, deī}} ('god') is irregular. The vocative singular of ''deus'' is not attested in Classical Latin. In [[Ecclesiastical Latin]] the vocative of ''Deus'' ('God') is ''Deus''.

In poetry, ''-um'' may substitute ''-ōrum'' as the genitive plural ending.

{| class="wikitable"
! rowspan="2" |
! colspan="2" | ''deus, deī''<br />god {{abbr|m.|masculine}}
|-
! Singular
! Plural
|-
! Nominative, Vocative
|deus ||deī<br />diī<br />dī
|-
! Accusative
| deum || deōs
|-
! Genitive
| deī || deōrum<br />deum
|-
! Dative, Ablative
| deō || deīs<br />diīs<br />dīs
|}

===== Virus =====
Three words, although second declension neuter, end in ''-us''. These are {{lang|la|vulgus}} "common people, crowd", {{lang|la|vīrus}} "slime, poison", and (borrowed from Greek) {{lang|la|pontus}} "sea".<ref>Ernout (1953), p. 34.</ref>

The word {{lang|la|vīrus}} means "1. slimy liquid, slime; 2. poison, venom", denoting the venom of a snake. This Latin word is probably related to the [[Greek language|Greek]] {{wikt-lang|grc|ῑ̓ός}} (''ios'') meaning "venom" or "rust" and the [[Sanskrit]] word {{wikt-lang|sa|विष}} ''{{Transliteration|sa|viṣa}}'' meaning "toxic, poison".<ref>Chambers' Etymological Dictionary Enlarged Edition 1931.</ref>

Since {{lang|la|vīrus}} in antiquity denoted something uncountable, it was a [[mass noun]]. Mass nouns pluralize only under special circumstances, hence the non-existence of plural forms in the texts.<ref>June 1999 issue of ASM News by the American Society for Microbiology</ref>

In [[Neo-Latin]], a plural form is necessary in order to express the modern concept of 'viruses', which leads to the following declension:<ref>[https://web.archive.org/web/20170728043240/interrete.de/latein/nuntiifinarch1.html Nuntii Latini: Finnish Broadcasting Company (Radiophonia Finnica Generalis). Archiv I. 19.5.2000 – 6.12.2002]: "NOVUM VIRUS COMPUTATORIUM<br />Novum viri computatorii genus nomine Code Red in praesenti in Interreti grassatur, ut nuntiavit institutum SANS, cuius est securitati retis informatici providere. Code Red II, quod per cursum electronicum diffunditur, priore viro acerbius est et, postquam in servitoria penetravit, in systema lacunam facit. Ita fieri potest, ut alia vira eaque etiam periculosiora in machinas computatorias irrepant. Iam vermis Code Red I molestissimus fuit, cum biduo in trecenta milia computatrorum in omni orbe terrarum invasit."</ref><ref>[https://de.pons.com/%C3%BCbersetzung?l=dela&q=virus Pons: ''virus'']</ref><ref>William T. Stearn: ''Botanical Latin. History, Grammar, Syntax, Terminology and Vocabulary.'' David & Charles, third edition, 1983. Quote: "Virus: virus (s.n. II), ''gen. sing.'' viri, ''nom. pl.'' vira, ''gen. pl.'' vīrorum (to be distinguished from ''virorum'', of men)."</ref>

{| class="wikitable"
! rowspan="2" |
! colspan="2" | ''{{wikt-lang|la|virus|vīrus, vīrī}}''<br />poison, venom, virus {{abbr|n.|neuter}}
|-
! Singular
! Plural
|-
! Nominative, Vocative, Accusative
| vīrus || vīra
|-
! Genitive
| vīrī{{efn-lr|antique, [[Proto-Indo-European nominals#Heteroclitic stems|heteroclitic]]: vīrus{{citation needed|date=November 2021}}}} || vīrōrum
|-
! Dative, Ablative
| vīrō || vīrīs
|}
{{notelist-lr}}

=== {{anchor|d3}} Third declension===
The third declension is the largest group of nouns. The nominative singular of these nouns may end in ''-a'', ''-e'', ''-ī'', ''-ō'', ''-y'', ''-c'', ''-l'', ''-n'', ''-r'', ''-s'', ''-t'', or ''-x''. This group of nouns includes masculine, neuter, and feminine nouns.

====Consonant stems====
The stem of a consonant-stem noun may be found from the genitive case by removing the ending ''-is''. For example, the stem of {{wikt-lang|la|pax|pāx, pācis}} {{abbr|f.|feminine}} 'peace' is ''pāc-,'' the stem of {{wikt-lang|la|flumen|flūmen, flūminis}} {{abbr|n.|neuter}} 'river' is ''flūmin-'', and the stem of {{wikt-lang|la|flos|flōs, flōris}} {{abbr|m.|masculine}} 'flower' is ''flōr-.''

Masculine, feminine and neuter nouns often have their own special nominative singular endings. For instance, many masculine nouns end in ''-or'' ({{wikt-lang|la|amor|amor, amōris}}, 'love'). Many feminine nouns end in ''-īx'' ({{wikt-lang|la|phoenix|phoenīx, phoenīcis}}, 'phoenix'), and many neuter nouns end in ''-us'' with an ''r'' stem in the oblique cases ({{wikt-lang|la|onus|onus, oneris}} 'burden'; {{wikt-lang|la|tempus|tempus, temporis}} 'time').

{| class="wikitable"
|+ Third declension paradigm<br />(consonant stems)
|-
! rowspan="2" |
! colspan="2" | Masculine &<br />feminine || colspan="2" | Neuter
|-
! Singular || Plural
! Singular || Plural
|-
! Nominative, Vocative
|(-s) || rowspan="2" | -ēs || rowspan="2" | —{{efn-lr|The nominative and accusative of neuter nouns are always identical.}} || rowspan="2" | -a
|-
! Accusative
| -em
|-
! Genitive
| -is || -um || -is || -um
|-
! Dative
| -ī || rowspan="2" | -ibus ||  -ī || rowspan="2" | -ibus
|-
! Ablative
| -e || -e
|-
! Locative
| ''Dat./Abl.'' || ''Dat.'' || ''Dat./Abl.'' || ''Dat.''
|}

{{notelist-lr}}

{| class="wikitable"
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|dux|dux, ducis}}<br />leader {{abbr|m.|masculine}}
! colspan="2" | {{wikt-lang|la|virtus|virtūs, virtūtis}}<br />virtue {{abbr|f.|feminine}}
! colspan="2" | {{wikt-lang|la|nomen|nōmen, nōminis}}<br />name {{abbr|n.|neuter}}
|-
! Singular
! Plural
! Singular
! Plural
! Singular
! Plural
|-
! Nominative, Vocative
|dux || rowspan="2" | ducēs ||virtūs || rowspan="2" | virtūtēs || rowspan="2" | nōmen || rowspan="2" | nōmina
|-
! Accusative
| ducem || virtūtem
|-
! Genitive
| ducis || ducum || virtūtis || virtūtum || nōminis || nōminum
|-
! Dative
| ducī || rowspan="2" | ducibus || virtūtī || rowspan="2" | virtūtibus || nōminī || rowspan="2" | nōminibus
|-
! Ablative
| duce || virtūte || nōmine
|}

The locative endings for the third declension are ''-ī'' or ''-e'' (singular) and ''-ibus'' (plural), as in {{wikt-lang|la|rus|rūrī}} 'in the country' and {{wikt-lang|la|Tralles|Trallibus}} 'at Tralles'.<ref>Allen and Greenough. §80.</ref>

==== {{anchor|d3i}} Third declension ''i''-stem and mixed nouns ====
The third declension also has a set of nouns that are declined differently. They are called '''''i''-stems'''. ''i''-stems are broken into two subcategories: pure and mixed. Pure ''i''-stems are indicated by special neuter endings. Mixed ''i''-stems are indicated by the double consonant rule. Stems indicated by the parisyllabic rule are usually mixed, occasionally pure.
;Masculine and feminine
:'''Parisyllabic rule:''' Some masculine and feminine third-declension ''i''-stem nouns have the same number of syllables in the genitive and the nominative. For example: {{wikt-lang|la|navis|nāvis, nāvis}} ('ship'); {{wikt-lang|la|nubes|nūbēs, nūbis}} ('cloud'). The nominative ends in ''-is'' or ''-ēs''.
:'''Double consonant rule:''' The rest of the masculine and feminine third-declension ''i''-stem nouns have two consonants before the ''-is'' in the genitive singular. For example: {{wikt-lang|la|pars|pars, partis}} ('part').
;Neuter
:'''Special neuter ending:''' Neuter third-declension ''i''-stems have no rule. However, all of them end in ''-al'', ''-ar'' or ''-e''. For example: {{wikt-lang|la|animal|animal, animālis}} ('animal'); {{wikt-lang|la|cochlear|cochlear, cochleāris}} ('spoon'); {{wikt-lang|la|mare|mare, maris}} ('sea').

The mixed declension is distinguished from the consonant type only by having ''-ium'' in the genitive plural (and occasionally ''-īs'' in the accusative plural). The pure declension is characterized by having ''-ī'' in the ablative singular, ''-ium'' in the genitive plural, ''-ia'' in the nominative and accusative plural neuter, and ''-im'' in the accusative singular masculine and feminine (however, adjectives have ''-em'').

The accusative plural ending ''-īs'' is found in early Latin up to [[Virgil]], but from the early empire onwards it was replaced by ''-ēs''.<ref name=":0">Gildersleeve & Lodge (1895), p. 18.</ref>

The accusative singular ending ''-im'' is found only in a few words: always in {{lang|la|tussis}} 'cough', {{lang|la|sitis}} 'thirst', {{lang|la|Tiberis}} 'River Tiber'; usually in {{lang|la|secūris}} 'axe', {{lang|la|turris}} 'tower', {{lang|la|puppis}} 'poop', {{lang|la|febris}} 'fever'; occasionally in {{lang|la|nāvis}} 'ship'. Most nouns, however, have accusative singular ''-em''.<ref>Gildersleeve & Lodge (1895), p. 27.</ref> The ending ''-im'' is not found in any adjectives, even those that have a separate feminine such as {{lang|la|celeris}} 'swift' or {{Lang|la|ācris}} 'keen',<ref>Ernout, A. (1953), {{lang|fr|Morphologie historique du latin}}, p. 50.</ref> or in any masculine common nouns.

The ablative singular ''-ī'' is found in nouns which have ''-im'', and also, optionally, in some other nouns, e.g. {{lang|la|in ignī}} or {{lang|la|in igne}} 'in the fire'.

There are two mixed-declension neuter nouns: {{wikt-lang|la|cor|cor, cordis}} ('heart') and {{wikt-lang|la|os|os, ossis}} ('bone'). The mixed declension is also used in the plural-only adjective  {{wikt-lang|la|plures|plūrēs, plūra}} ('most').

{| class="wikitable"
|+ Third declension paradigm<br />(''i''-stem nouns)
|-
! rowspan="2" |
! colspan="2" | Masculine &<br />Feminine || colspan="2" | Neuter
|-
! Singular || Plural
! Singular || Plural
|-
! Nominative, Vocative
|— ||-ēs || rowspan="2" | — || rowspan="2" | -ia
|-
! Accusative
| -em<br />-im || -ēs<br />-īs
|-
! Genitive
| -is || -ium || -is || -ium
|-
! Dative
| -ī || rowspan="2" | -ibus || rowspan="2" | -ī || rowspan="2" | -ibus
|-
! Ablative
| -e<br />-ī
|-
! Locative
| ''Dat./Abl.'' || ''Dat.'' || ''Dat./Abl.'' || ''Dat.''
|}

{| class="wikitable"
|+ Third declension paradigm<br />(mixed nouns)
|-
! rowspan="2" |
! colspan="2" | Masculine &<br />Feminine || colspan="2" | Neuter
|-
! Singular || Plural
! Singular || Plural
|-
! Nominative, Vocative
|— ||-ēs || rowspan="2" | — || rowspan="2" | -a
|-
! Accusative
| -em || -ēs<br />-īs
|-
! Genitive
| -is || -ium || -is || -ium
|-
! Dative
| -ī || rowspan="2" | -ibus || -ī || rowspan="2" | -ibus
|-
! Ablative
| -e || -e
|-
! Locative
| ''Dat./Abl.'' || ''Dat.'' || ''Dat./Abl.'' || ''Dat.''
|}

{| class="wikitable"
! rowspan="3" |
! colspan="2" | {{wikt-lang|la|turris|turris, turris}}<br />tower {{abbr|f.|feminine}} (pure)
! colspan="2" | {{wikt-lang|la|pars|pars, partis}}<br />part, piece {{abbr|f.|feminine}} (mixed)
! colspan="2" | {{wikt-lang|la|animal|animal, animālis}}<br /> animal, living being {{abbr|n.|neuter}} (pure)
|-
! colspan="2" | Parisyllabic rule
! colspan="2" | Double consonant rule
! colspan="2" | Special neuter ending
|-
! Singular
! Plural
! Singular
! Plural
! Singular
! Plural
|-
! Nominative,  Vocative
|turris||turrēs ||pars ||partēs || rowspan="2" | animal || rowspan="2" | animālia
|-
! Accusative
| turrem<br />turrim || turrēs<br />turrīs || partem || partēs<br />partīs
|-
! Genitive
| turris || turrium || partis || partium || animālis || animālium
|-
! Dative
| turrī || rowspan="2" | turribus || partī || rowspan="2" | partibus || rowspan="2" | animālī || rowspan="2" | animālibus
|-
! Ablative
| turre<br />turrī || parte<br />(partī)
|}

The rules for determining ''i''-stems from non-''i''-stems and mixed ''i''-stems are guidelines rather than rules: many words that might be expected to be ''i''-stems according to the parisyllabic rule actually are not, such as {{wikt-lang|la|canis}} ('dog') or {{wikt-lang|la|iuvenis}} ('youth'), which have genitive plural {{lang|la|canum}} 'of dogs' and {{lang|la|iuvenum}} 'of young men'. Likewise, {{wikt-lang|la|pater}} ('father'), {{wikt-lang|la|māter}} ('mother'), {{wikt-lang|la|frāter}} ('brother'), and {{wikt-lang|la|parēns}} ('parent') violate the double-consonant rule. This fluidity even in Roman times resulted in much more uncertainty in Medieval Latin.

Some nouns in ''-tāt-'', such as {{wikt-lang|la|civitas|cīvitās, cīvitātis}} 'city, community' can have either consonant-stem or ''i''-stem genitive plural: {{lang|la|cīvitātum}} or {{lang|la|cīvitātium}} 'of the cities'.<ref name=":0"/>

==== Peculiarities ====
In the third declension, there are four irregular nouns.
{| class="wikitable"
|-
!rowspan="2" | Case
! colspan="2" | {{wikt-lang|la|vis|vīs, vīs}} <br /> force, power {{abbr|f.|feminine}}
! colspan="2" | {{wikt-lang|la|sus|sūs, suis}} <br /> swine, pig, hog {{abbr|m.f.|masculine and feminine}}
! colspan="2" | {{wikt-lang|la|bos|bōs, bovis}} <br /> ox, bullock {{abbr|m.f.|masculine and feminine}}
! {{wikt-lang|la|Iuppiter|Iuppiter, Iovis}} <br /> Jupiter {{abbr|m.|masculine}}
|-
! Singular || Plural || Singular || Plural || Singular || Plural || Singular
|-
! Nominative, Vocative
|vīs ||vīrēs ||sūs || rowspan="2" | suēs ||bōs{{efn-lr|name="ou"|Here ''ō'' or ''ū'' come from Old Latin ''ou''. Thus ''bō-/bū-'' and ''Iū-'' before consonant endings are alternate developments of the ''bov-'' and ''Iov-'' before vowel endings. — The double ''pp'' in the preferred form ''Iu-ppiter'' "Father Jove" is an alternate way of marking the length of the ''u'' in the etymological form ''Iū-piter'' (see footnote in [[Jupiter (mythology)]]). ''i'' is [[vowel reduction|weakened]] from ''a'' in {{wikt-lang|la|pater}} (Allen and Greenough, sect. 79 b).}} || rowspan="2" | bovēs ||Iuppiter<br />Iūpiter{{efn-lr|name="ou"}}
|-
! Accusative
| '''vim''' || vīrēs<br />vīrīs || suem || bovem || Iovem
|-
! Genitive
| vīs{{efn-lr|name="vis"|Genitive and dative cases are seldom used.}} || '''vīrium''' || suis || suum || bovis || '''boum'''<br />'''bovum''' || Iovis
|-
! Dative
| rowspan="2" | vī{{efn-lr|name="vis"}} || rowspan="2" | vīribus || suī || rowspan="2" | suibus<br />'''sūbus''' || bovī || rowspan="2" | '''bōbus'''<br />'''būbus'''{{efn-lr|name="ou"}} || Iovī
|-
! Ablative
| sue || bove || Iove
|}
{{notelist-lr}}

=== {{anchor|d4}}{{anchor|Fourth declension}} Fourth declension (''u'' stems) ===
The fourth declension is a group of nouns consisting of mostly masculine words such as {{wikt-lang|la|flūctus|flūctus, flūctūs}} {{abbr|m.|masculine}} ('wave') and {{wikt-lang|la|portus|portus, portūs}} {{abbr|m.|masculine}} ('port') with a few feminine exceptions, including {{wikt-lang|la|manus|manus, manūs}} {{abbr|f.|feminine}} ('hand') and {{wikt-lang|la|domus|domus, domūs}} {{abbr|f.|feminine}} ('house'). The fourth declension also includes several neuter nouns including {{wikt-lang|la|genu|genū, genūs}} {{abbr|n.|neuter}} ('knee'). Each noun has the ending ''-ūs'' as a suffix attached to the root of the noun in the genitive singular form. The predominant letter in the ending forms of this declension is ''u'', but the declension is otherwise very similar to the third-declension ''i'' stems.

{| class="wikitable"
|+ Fourth declension paradigm
|-
! rowspan="2" |
! colspan="2" | ''-us'' ending nouns || colspan="2" | ''-ū'' ending nouns
|-
! Singular || Plural
! Singular || Plural
|-
! Nominative, Vocative
| -us || rowspan="2" | -ūs || rowspan="2" | -ū || rowspan="2" | -ua
|-
! Accusative
| -um
|-
! Genitive
| -ūs || -uum || -ūs || -uum
|-
! Dative
| -uī || rowspan="2" | -ibus<br>-ubus{{efn-lr|used only on bisyllabic words like {{wikt-lang|la|arcus}} and {{wikt-lang|la|artus}}.}} || rowspan="2" | -ū || rowspan="2" | -ibus
|-
! Ablative
| -ū
|-
! Locative
| -ī  || ''Dat.'' || -ī || ''Dat.''
|}

{{notelist-lr}}

{| class="wikitable"
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|portus|portus, portūs}}<br /> port {{abbr|m.|masculine}}
! colspan="2" | {{wikt-lang|la|genu|genū, genūs}}<br /> knee {{abbr|n.|neuter}}
|-
! Singular
! Plural
! Singular
! Plural
|-
! Nominative, Vocative
|portus || rowspan="2" | portūs || rowspan="2" | genū || rowspan="2" | genua
|-
! Accusative
| portum
|-
! Genitive
| portūs || portuum || genūs || genuum
|-
! Dative
| portuī || rowspan="2" | portibus || rowspan="2" |genū || rowspan="2" | genibus
|-
! Ablative
| portū
|}

* In the genitive singular, ''cornūs'' may in later times be replaced by ''cornū''.
* The locative endings for the fourth declension are ''-ī'' (singular) and ''-ibus'' (plural); {{wikt-lang|la|senatus|senātī}} "at [the] senate", {{wikt-lang|la|domus|domī}} "at home".

====Domus====
{{wikt-lang|la|domus|Domus}} ('house, dwelling, building, home, native place, family, household, race') is an irregular noun, mixing fourth and second declension nouns at the same time (especially in literature). However, in practice, it is generally declined as a regular ''-us'' stem fourth declension noun, except for ablative singular ''-ō'', accusative plural ''-ōs'', and the use of the locative.<ref>[https://www.youtube.com/watch?v=33n1qYq9Liw The Fourth Declension] – tutorial by Ben Johnson of [https://latintutorial.com/about LatinTutorial]</ref>

{| class="wikitable"
! rowspan="3" |
! colspan="2" | {{wikt-lang|la|domus|domus, domūs/domī}} {{abbr|f.|feminine}}
|-
! colspan="2" | All possible declensions
|-
! Singular
! Plural
|-
! Nominative, Vocative
|domus ||domūs
|-
! rowspan="2" | Accusative
| rowspan="2" | domum || domōs
|-
|domūs
|-
! rowspan="2" | Genitive
| domūs || domuum
|-
|domī
|domōrum
|-
! rowspan="3" | Dative
| domuī || rowspan="6" | domibus
|-
|domō
|-
| rowspan="2" |domō
|-
! rowspan="2" |Ablative
|-
|domū
|-
! Locative
| domī
|}
{| class="wikitable"
! rowspan="3" |
! colspan="2" | {{wikt-lang|la|domus|domus, domūs}} {{abbr|f.|feminine}}
|-
! colspan="2" | Most common paradigm
|-
! Singular
! Plural
|-
! Nominative, Vocative
|domus ||domūs
|-
! Accusative
| domum || domōs
|-
! Genitive
| domūs || domuum
|-
! Dative
| domuī || rowspan="3" | domibus
|-
! Ablative
| domō
|-
! Locative
| domī
|}
{{notelist-lr}}

=== {{anchor|d5}}{{anchor|Fifth declension}} Fifth declension (''e'' stems) ===
The fifth declension is a small group of nouns consisting of mostly feminine nouns like {{wikt-lang|la|res|rēs, reī}} {{abbr|f.|feminine}} ('affair, matter, thing') and ''diēs, diēī'' {{abbr|m.|masculine}} ('day'; but {{abbr|f.|feminine}} in names of days).

{| class="wikitable"
|+ Fifth declension paradigm
|-
! rowspan="2" |
! colspan="2" | ''-iēs'' ending nouns || colspan="2" | ''-ēs'' ending nouns
|-
! Singular || Plural
! Singular || Plural
|-
! Nominative, Vocative
| -iēs || rowspan="2" | -iēs ||-ēs || rowspan="2" | -ēs
|-
! Accusative
| -iem || -em
|-
! Genitive
| rowspan="2" | -iēī || -iērum || rowspan="2" | -eī || -ērum
|-
! Dative
| rowspan="2" | -iēbus  || rowspan="2" | -ēbus
|-
! Ablative, Locative
| -iē || -ē
|}
{| class="wikitable"
! rowspan="2" |
! colspan="2" | {{wikt-lang|la|dies|diēs, diēī}}<br />day {{abbr|m.|masculine}}, {{abbr|f.|feminine}}
! colspan="2" | {{wikt-lang|la|res|rēs, reī}}<br />thing {{abbr|f.|feminine}}
|-
! Singular
! Plural
! Singular
! Plural
|-
! Nominative, Vocative
|diēs || rowspan="2" | diēs ||rēs || rowspan="2" | rēs
|-
! Accusative
| diem || rem
|-
! Genitive
| rowspan="2" | diēī || diērum || rowspan="2" | reī || rērum
|-
! Dative
| rowspan="2" | diēbus || rowspan="2" | rēbus
|-
! Ablative, Locative
| diē || rē
|}
Nouns ending in ''-iēs'' have long ''ēī'' in the dative and genitive, while nouns ending in a consonant + ''-ēs'' usually have short ''eī'' in these cases. Other forms of the genitive singular are also found, such as {{lang|la|diī}} (''Aeneid'' 1.636), {{lang|la|diē}} (''Georgic'' 1.208), {{lang|la|diēs}} (Ennius).<ref>Ernout (1953), p. 69.</ref>

The locative ending of the fifth declension was ''-ē'' (singular only), identical to the ablative singular, as in {{wikt-lang|la|hodiē}} ('today').