Where does “четвьртъ” come from?
четвьртъ (Old East Slavic) comes from Proto-Slavic četvьrtъ, from Proto-Balto-Slavic ketwirtas, from Proto-Indo-European *kʷetwr̥tós.
четвьртъ (Old East Slavic): fourth
Ancestry of “четвьртъ”, step by step
Words derived from “четвьртъ”