Where does “jest” come from?

jest (Czech) comes from Old Czech jest, from Proto-Slavic estь, from Proto-Balto-Slavic *esti, from Proto-Indo-European *h₁ésti.

Ancestry of “jest”, step by step

StepLanguageWordMeaning
1Old Czechjest—
2Proto-Slavicestьestь; third-person singular present active...
3Proto-Balto-Slavic*esti—
4Proto-Indo-European*h₁ésti—
Every word from Proto-Indo-European *h₁ésti →Every word from Proto-Balto-Slavic *esti →Every word from Proto-Slavic estь →