aššum - concerning, on behalf of, on account of, because of, with respect to, related to (CAD A₂ 467, AHw. 84)

Likely from ana šumi (lit. ‘for the name’, see GAG 207, CDG 43). See also the expression ana šumi ‘because of, as for’ (CAD Š₃ 294, AHw. 295), in which both lexemes are used separately.

*ˀVSVm - because of, for the sake of (Arakelova 2001:30)
The sibilant is uncertain.
Both Akk. and Gez. forms are likely related to the noun *šVm- ‘name’.