The etymology is uncertain, probably a borrowing from Sum. gìb (Kogan & Krebernik 2021: 398)
With k < *ḳ by dissimilation of two «emphatic» consonants.
The form kiṣṣu would exactly correspond to Gez. ḳʷəyṣ, ḳʷəṣ if not for the fact that it can hardly be separated from the Akk forms with m and n, of which kimṣu looks a primary one (cf. also kamāsu, kamāṣu ‘to squat, kneeľ).