Where does “þriē” come from?

þriē (Old English) comes from Proto-West Germanic þrīʀ, from Proto-Germanic þrīz, from Proto-Indo-European *tréyes.

Ancestry of “þriē”, step by step

StepLanguageWordMeaning
1Proto-West Germanicþrīʀthree
2Proto-Germanicþrīzthree
3Proto-Indo-European*tréyes—
Every word from Proto-Indo-European *tréyes →Every word from Proto-Germanic þrīz →Every word from Proto-West Germanic þrīʀ →