Where does “(s)pjāˀu-” come from?

(s)pjāˀu- (Proto-Balto-Slavic) comes from Proto-Indo-European (s)ptyēw- — to spit, vomit.

Ancestry of “(s)pjāˀu-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	(s)ptyēw-	to spit, vomit