Where does “köpür-” come from?

köpür- (Old Turkic) comes from Proto-Turkic köp- — to swell; foam; to swell, surge.

Ancestry of “köpür-”, step by step

Step	Language	Word	Meaning
1	Proto-Turkic	köp-	to swell; foam; to swell, surge

köpür- — Etymology, Origin & Word History | Etymology Explorer