Where does “kъlkъ” come from?

kъlkъ (Proto-Slavic) comes from Proto-Balto-Slavic kaukāˀ, from Proto-Indo-European klHk(ᵂ)-(n)-.

Ancestry of “kъlkъ”, step by step

Step	Language	Word	Meaning
1	Proto-Balto-Slavic	kaukāˀ	—
2	Proto-Indo-European	klHk(ᵂ)-(n)-	—

kъlkъ — Etymology, Origin & Word History | Etymology Explorer