PS

*ḫam/nṣ- - waist (SED I No. 132)

Scarcely attested (in Akk. and Arb.); phonetically and semantically highly problematic. Vocalism based on Akk. only, as the Arb. form represents a derived pattern.

Akkadian
ḫanṣātu - part of human body, possibly waist (CAD ḫ 81, AHw 321)
(pl. t.), Possibly < *ḫamṣātu (on n < m before sibilants in Akk. see [GAG 40]).
Arabic
ˀaḫmaṣ- - middle of the body, slim mid body (BK 1 633)
Cf. ḫmṣ ‘to be empty (said of the belly); de-swelling (said of a wound from which the swelling goes away)’ [ibid.] (cf. the latter meaning also in ḫmṣ [ibid. 492])
Soqotri
mónḥeṣ - small of the back (LS 264; CSOL I 623)

Likely related with metathesis