There is no consensus about the etymology. Comparison with the fossilized negative element ˀən- in Geez (Leslau 1958:10, 1969:144, CDG 27) is problematic since *-ay- is not expected to be reduced to ə. The phonologically transparent equation with Arb. ˀayna ‘where’ (HALOT 41) presupposes a semantic shift from rhetorical question to negation. If this etymology is accepted, the innovative nature of PC *ˀayn- is evident. Still another possibility is to identify *ˀayna with the PS negative element *ˀay/*ˀī , in which case the innovation (addition of -n) becomes formal rather than semantic (cf. Faber 1991:416).
see also Akk yānu - there is not