The Collaborative International Dictionary of English v.0.48:

Nipper \Nip"per\, n.
   1. One who, or that which, nips.
      [1913 Webster]

   2. A fore tooth of a horse. The nippers are four in number.
      [1913 Webster]

   3. A satirist. [Obs.] --Ascham.
      [1913 Webster]

   4. A pickpocket; a young or petty thief. [Old Cant]
      [1913 Webster]

   5. (Zool.)
      (a) The cunner.
      (b) A European crab (Polybius Henslowii).
          [1913 Webster]

WordNet (r) 3.0 (2006):

nipper
    n 1: a young person of either sex; "she writes books for
         children"; "they're just kids"; "`tiddler' is a British
         term for youngster" [syn: child, kid, youngster,
         minor, shaver, nipper, small fry, tiddler,
         tike, tyke, fry, nestling]
    2: a grasping structure on the limb of a crustacean or other
       arthropods [syn: claw, chela, nipper, pincer]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "nipper":
   bairn, bud, cherub, chick, chickabiddy, child, chit, claws,
   clutches, darling, digits, fangs, fingernails, fingers, hands,
   hooks, innocent, jaws, juvenile, kid, kitten, lamb, lambkin,
   little bugger, little fellow, little guy, little innocent,
   little one, little tad, little tot, mandibles, maxillae, meathooks,
   mite, mitts, moppet, nails, nippers, offspring, palm, peewee,
   pincers, pounces, shaver, tad, talons, teeth, tot, unguals,
   ungulae, wee tot, youngling, youngster