Where does “jsou” come from?

jsou (Czech) comes from Old Czech jsú, from Proto-Slavic sǫtь.

Ancestry of “jsou”, step by step

StepLanguageWordMeaning
1Old Czechjsú—
2Proto-Slavicsǫtь—
Every word from Proto-Slavic sǫtь →Every word from Old Czech jsú →
jsou — Etymology, Origin & Word History | Etymology Explorer