Where does “они” come from?

они (Old East Slavic) comes from Proto-Slavic *onъ, from Proto-Balto-Slavic anas, from Proto-Indo-European h₂en — there.

Ancestry of “они”, step by step

StepLanguageWordMeaning
1Proto-Slavic*onъ—
2Proto-Balto-Slavicanasthat over there, yonder
3Proto-Indo-Europeanh₂enthere

Words derived from “они”

Every word from Proto-Indo-European h₂en →Every word from Proto-Balto-Slavic anas →Every word from Proto-Slavic *onъ →