The Collaborative International Dictionary of English v.0.48:

Mouthful \Mouth"ful\, n.; pl. Mouthfuls.
   1. As much as is usually put into the mouth at one time.
      [1913 Webster]

   2. Hence, a small quantity.
      [1913 Webster]

   3. A statement that has a profound truth in it; as, you said
      a mouthful! [informal]
      [PJC]

WordNet (r) 3.0 (2006):

mouthful
    n 1: the quantity that can be held in the mouth
    2: a small amount eaten or drunk; "take a taste--you'll like it"
       [syn: taste, mouthful]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "mouthful":
   bellyful, bit, bite, bolus, bumper, capacity, champ, charge, chaw,
   chew, chomp, chunk, complement, cram, crush, cud, fill, full house,
   full measure, gnash, gob, hard words, high-sounding words, hunk,
   jam up, jawbreaker, jawtwister, lading, lexiphanicism, load,
   long word, lump, morsel, munch, nibble, nip,
   pneumonoultramicroscopicsilicovolcanoconiosis, polysyllabism, quid,
   sesquipedalian word, sesquipedalianism, sesquipedality, skinful,
   snap, snootful, spoonful, swallow, technical jargon,
   two-dollar word