c. 1300, "to bite or snap" (of a dog), probably from Middle Dutch or Flemish snacken "to snatch, snap; chatter," which Watkins traces to a hypothetical Germanic imitative root *snu- forming words having to do with the nose (see snout). The meaning "have a mere bite or morsel, eat a light meal" is first attested 1807. Related: Snacked; snacking.
c. 1400, "a snatch or snap" (especially that of a dog), from snack (v.). Later "a snappish remark" (1550s); "a share, portion, part" (1680s; hence old expression go snacks "share, divide; have a share in"). Main modern meaning "a bite or morsel to eat hastily" is attested from 1757. Snack bar is attested from 1923. Commercial plural form snax attested from 1942 in the vending machine trade.