Outside Aramaic, aphaeresis of ˀa- in PS *ˀaḥad- ‘one’ is regular in some varieties of modern EthS (v. EDG 322 under Sel. Zwy. had).
See also PWS *ḥyw ‘to live’ and Arb. ḥayyat- 'snake'. For the semantic development “animal” > “snake” v. extensively SED II No. 159 and Kogan 2015:300.
the origin is uncertain
contra Sum. gu-za, Akk. kussiˀu, Hbr. kissē(ˀ)