Editing Sigma (section)

{{Short description|Eighteenth letter of the Greek alphabet}}
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{{about|uses of the Greek letter}}
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{{Not to be confused with|Stigma (disambiguation){{!}}Stigma}}
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{{Greek alphabet|letter=sigma}}

'''Sigma ''' ({{IPAc-en|'|s|ɪ|g|m|ə|audio=LL-Q1860 (eng)-Flame, not lame-Sigma.wav}} {{respell|SIG|mə}};<ref>{{OED|sigma}}</ref> [[uppercase]] '''Σ''', [[lowercase]] '''σ''', lowercase in word-final position '''ς'''; {{langx|grc|σίγμα}}) is the eighteenth letter of the [[Greek alphabet]]. In the system of [[Greek numerals]], it has a value of 200. In general mathematics, uppercase '''Σ''' is used as an [[operator (mathematics)|operator]] for [[summation]]. When used at the end of a [[Letter case|letter-case]] word (one that does not use [[all caps]]), the [[final form]] (ς) is used. In ''{{Langx|grc|Ὀδυσσεύς|label=none}}'' (Odysseus), for example, the two lowercase sigmas (σ) in the center of the name are distinct from the word-final sigma (ς) at the end. The [[Latin alphabet|Latin]] letter [[S]] derives from sigma while the [[Cyrillic script|Cyrillic]] letter [[Es (Cyrillic)|Es]] derives from a [[#Lunate sigma|lunate form]] of this letter.