The origin is Vörlaag:unk.. What follows is Matasović’s summary of opinions.
Some scholars (e.g. Meillet and Godel) take the obvious course and derive it from Proto-Indo-Europääsch masuline-feminine plural nominative case ending *-s, but the sound development of word final *-s to *-ք (*-kʿ) is not universally accepted. Other linguists assume a pronominal particle added to the bare stem, but the origin of that particle has never been explained. A recent hypothesis derives -ք (-kʿ) from the agglutinated Proto-Indo-Europääsch *dwóh₁ (“two”); it would have been originally a dual marker, subsequently replacing the inherited plural. Another possibility, which is a mere speculation: the plural marker -ք (-kʿ) can be regularly derived from *-s-wes, with the ending of the u-stems *-w-es agglutinated to the regular nominative plural marker *-s.
- plural nominative case marker
- forming names of countries