Where does “wēsus” come from?

wēsus (Proto-Balto-Slavic) comes from Proto-Indo-European wē- — to winnow, thresh; to blow, to breathe.

Ancestry of “wēsus”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	wē-	to winnow, thresh; to blow, to breathe

wēsus — Etymology, Origin & Word History | Etymology Explorer