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.