The Collaborative International Dictionary of English v.0.48:

Snack \Snack\, n. [See Snatch, v. t.]
   1. A share; a part or portion; -- obsolete, except in the
      colloquial phrase, to go snacks, i. e., to share.
      [1913 Webster]

            At last he whispers, "Do, and we go snacks." --Pope.
      [1913 Webster]

   2. A slight, hasty repast. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

snack
    n 1: a light informal meal [syn: bite, collation, snack]
    v 1: eat a snack; eat lightly; "She never loses weight because
         she snacks between meals" [syn: nosh, snack]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "snack":
   bait, bit, bite, butt, chip, chunk, clip, clipping, collation,
   collop, crumb, cut, cutting, dollop, elevenses, end, fragment, gob,
   gobbet, hunk, light lunch, light meal, light repast, lump, modicum,
   moiety, morsel, nibble, nosh, paring, particle, peck, peck at,
   pick, pick at, piece, rasher, refreshment, refreshments, scoop,
   scrap, shard, shaving, shiver, shred, slice, sliver, smithereen,
   snatch, snip, snippet, splinter, spot of lunch, stitch, stump,
   tatter, tea