Has been envisioned as from Proto-Semitic *kaʔs-. The Arabic form could be a hypercorrection after a borrowing from the Aramaic forms listed under it however, since inheritance of Akkadian 𒃲 (kāsum) from such a proto-form is irregular as one expects vocalism like in Akkadian 𒊕 (rēšum) from Proto-Semitic *raʔš-, so also considering the absence in Ethiopian Semitic one may conclude a post-Proto-Semitic external borrowing.