Where does “ծաղ-” come from?

ծաղ- (Old Armenian) comes from Proto-Indo-European ǵl̥h₂-.

Ancestry of “ծաղ-”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	ǵl̥h₂-	—

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