Russian кой

← Proto-Balto-Slavic *kas (derived)

← Proto-Indo-European *kʷe- (root)

← Proto-Indo-European *kʷos (derived)

← Old East Slavic кꙑи (inherited)

← Proto-Slavic *kъjь (inherited)

← Proto-Slavic *kъ (mention)

← Proto-Slavic *-jь (mention)