The term is often thought to be borrowed from Sum. UZ, but the Sum. term itself is likely to be an early Semitism (as suggested in Landsberger 1966: 257, cf. also Salonen 1973: 288-9).
Var. šummu (known from later texts only). According to Englund 1995 45 ff. u. is to be identified with the bandicoot rat rather than dormouse as previously thought.