Where does “рꙋчаи” come from?

рꙋчаи (Old East Slavic) comes from Proto-Slavic ručajь, from Proto-Slavic -ějь, from Proto-Balto-Slavic -ēˀjas.

Ancestry of “рꙋчаи”, step by step

StepLanguageWordMeaning
1Proto-Slavicručajьcrook, brook
2Proto-Slavic-ějьDeverbal from stative verbs inflecting in *-ěti....
3Proto-Balto-Slavic-ēˀjas—
Every word from Proto-Balto-Slavic -ēˀjas →Every word from Proto-Slavic -ějь →Every word from Proto-Slavic ručajь →