Likely a semantic shift; for a similar shift, cf. Ugr. yd, Hbr. yād ‘hand’ and
‘penis’ [HALOT 387]; and Arm. Jud. ˀammətā ‘cubit; membrum virile’ [Jastrow 79] (see *ˀamm-at- ‘elbow, forearm’, No. 6).
A phonetic diversity throughout Sem. can be explained by (1) lower compatibility of a voiced and voiceless stop in Hbr. and Arm., and (2) change of *m > n in contact with -d (for a similar phonetic evolution cf. *p/ban/md(at) ‘back, podex’,
No. 216).