The Collaborative International Dictionary of English v.0.48:

Barb \Barb\ (b[aum]rb), n. [F. barbe, fr. L. barba beard. See
   Beard, n.]
   1. Beard, or that which resembles it, or grows in the place
      of it.
      [1913 Webster]

            The barbel, so called by reason of his barbs, or
            wattles in his mouth.                 --Walton.
      [1913 Webster]

   2. A muffler, worn by nuns and mourners. [Obs.]
      [1913 Webster]

   3. pl. Paps, or little projections, of the mucous membrane,
      which mark the opening of the submaxillary glands under
      the tongue in horses and cattle. The name is mostly
      applied when the barbs are inflamed and swollen. [Written
      also barbel and barble.]
      [1913 Webster]

   4. The point that stands backward in an arrow, fishhook,
      etc., to prevent it from being easily extracted. Hence:
      Anything which stands out with a sharp point obliquely or
      crosswise to something else. "Having two barbs or points."
      --Ascham.
      [1913 Webster]

   5. A bit for a horse. [Obs.] --Spenser.
      [1913 Webster]

   6. (Zool.) One of the side branches of a feather, which
      collectively constitute the vane. See Feather.
      [1913 Webster]

   7. (Zool.) A southern name for the kingfishes of the eastern
      and southeastern coasts of the United States; -- also
      improperly called whiting.
      [1913 Webster]

   8. (Bot.) A hair or bristle ending in a double hook.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Barbel \Bar"bel\ (b[aum]r"b[e^]l), n.[OF. barbel, F. barbeau,
   dim. of L. barbus barbel, fr. barba beard. See 1st Barb.]
   [1913 Webster]
   1. (Zool.) A slender tactile organ on the lips of certain
      fishes.
      [1913 Webster]

   2. (Zool.) A large fresh-water fish (Barbus vulgaris) found
      in many European rivers. Its upper jaw is furnished with
      four barbels.
      [1913 Webster]

   3. pl. Barbs or paps under the tongues of horses and cattle.
      See 1st Barb, 3.
      [1913 Webster]

WordNet (r) 3.0 (2006):

barbel
    n 1: slender tactile process on the jaws of a fish [syn:
         barbel, feeler]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "barbel":
   antenna, barb, barbule, bristle, cat whisker, feeler, palp, palpus,
   setula, setule, striga, stubble, tactile cell, tactile corpuscle,
   tactile hair, tactile organ, tactile process, tactor, vibrissa