From Proto-Italic *kelō, from Proto-Indo-European *kelh₁- (“to call, shout”).
Cognate with Latin clāmō, clārus, classis, concilium, Ancient Greek καλέω (kaléō), Old English hlōwan (“to make a loud noise, roar, bellow”) (whence English low (“to moo”)). Another possible cognate is Proto-Slavic *kolkolъ (“bell”). Not related to call.