Proto-Altaic: *ìlù
Meaning: third (or next after three), consisting of three objects
Russian meaning: третий (или четвертый после трех), состоящий из трех предметов
Comments: An interesting etymon; the original meaning can be probably reconstructed as "(a group of) three objects, followed by a fourth". The Turkic form must represent a vowel assimilation < *ilöŋ.