Akk.-Ugr. *kms is vaguely reminiscent of Akkadian and WS anatomic terms denoting “articulation,” “joint” (Akk. kimṣu, Hbr. ḳəmāṣīm, see SED I No. 172), but no phonologically exact cognate has been detected so far.
Cf. Ugr. kms ‘to buckle, to bend’ (Kogan 2015: 336)
Ugaritic
kms - to buckle, to bend
(DUL 446, Watson 2007: 88)
As reasonably surmised in HALOT 1109, it is to this root that the Ugaritic verb ḳmṣ ‘to curl up, to bend’ likely belongs. This comparison invalidates Watson’s conclusion that Ugr. ḳmṣ is borrowed from Akkadian (Watson 2007:101).