Where does “-о-” come from?

-о- (Bulgarian) comes from Old Church Slavonic -о-, from Proto-Slavic -o-.

Ancestry of “-о-”, step by step

StepLanguageWordMeaning
1Old Church Slavonic-о-—
2Proto-Slavic-o-—

Words derived from “-о-”

Every word from Proto-Slavic -o- →Every word from Old Church Slavonic -о- →