Where does “tri” come from?

tri (Old Breton) comes from Proto-Brythonic tri, from Proto-Celtic trīs, from Proto-Indo-European *tréyes.

Ancestry of “tri”, step by step

StepLanguageWordMeaning
1Proto-Brythonictrithree
2Proto-Celtictrīsthree
3Proto-Indo-European*tréyes—

Words derived from “tri”

Every word from Proto-Indo-European *tréyes →Every word from Proto-Celtic trīs →Every word from Proto-Brythonic tri →