Where does “tři” come from?

tři (Old Czech) comes from Proto-Slavic tri, from Proto-Balto-Slavic tríjes, from Proto-Indo-European *tréyes.

Ancestry of “tři”, step by step

StepLanguageWordMeaning
1Proto-Slavictri—
2Proto-Balto-Slavictríjesthree
3Proto-Indo-European*tréyes—

Words derived from “tři”

Every word from Proto-Indo-European *tréyes →Every word from Proto-Balto-Slavic tríjes →Every word from Proto-Slavic tri →