Comments:АПиПЯЯ 109, 277, Мудрак Дисс. 103 (see also *gi̯ūbe, *ki̯àjú, with a possibility of contaminations). Note that both in MMong. and OJ the root is sometimes treated as borrowed from MChin. khɨ̀j (see, e.g., Rozycki 139) - which is not totally excluded, but somewhat dubious (very early attestation both in Mongolian and Japanese texts, and unexplained vocalism).
