Copulative a
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The copulative a (also a copulativum, a athroistikon) is the prefix {{#invoke:Lang|lang}} (Template:Translit) or {{#invoke:Lang|lang}} (Template:Translit) used to express unity in Ancient Greek, derived from Proto-Indo-European Template:PIE, cognate to English same (see also symbel).<ref name="a">Template:LSJ.</ref>
An example is {{#invoke:Lang|lang}} (Template:Translit 'brother'), from Template:PIE, literally meaning 'from the same womb' (compare Delphi).
In Proto-Greek, the Proto-Indo-European phoneme Template:PIE at the beginning of a word became {{#invoke:Lang|lang}} by debuccalization and syllabic Template:PIE became {{#invoke:Lang|lang}}, giving the combined form {{#invoke:Lang|lang}}. The initial {{#invoke:Lang|lang}} was sometimes lost by psilosis or Grassmann's law.
Cognate forms in other languages preserve the original Proto-Indo-European Template:PIE. For example, the Sanskrit prefix Template:Translit occurs in the name of the language, {{#invoke:Lang|lang}} Template:Translit, literally 'put together'. Less exact cognates include English same and some, and Latin {{#invoke:Lang|lang}} 'at the same time' and {{#invoke:Lang|lang}} 'similar'.<ref>Template:OEtymD</ref><ref>Template:OED</ref>
Other words in Greek are related, including {{#invoke:Lang|lang}} (Template:Translit 'at the same time'), {{#invoke:Lang|lang}} (Template:Translit 'same'), and {{#invoke:Lang|lang}} (Template:Translit 'one'; from Proto-Indo-European Template:PIE).<ref name="a" /><ref>Template:LSJ, Template:LSJ, Template:LSJ.</ref>