Probably from Akkadian (i.e., Assyrian!)
simānu; see
AIOA 91f. A. Panaino has recently argued instead for an Old Iranian origin in
Iran and the Caucasus 21(2017): 150ff.; however his understanding of the phonology and semantics of the Semitic material is weak. Rather the expansion of the idea from 'set time' to the abstract idea within Iranian is native and has influenced only Syriac usage, for which
see also s.v.
zbn #2.