Where does “ϑel(u)-” come from?

ϑel(u)- (Proto-Albanian) comes from Proto-Indo-European ḱelH- — to freeze.

Ancestry of “ϑel(u)-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	ḱelH-	to freeze

ϑel(u)- — Etymology, Origin & Word History | Etymology Explorer