The Collaborative International Dictionary of English v.0.48:

Dancer \Dan"cer\, n.
   One who dances or who practices dancing.
   [1913 Webster]

   The merry dancers, beams of the northern lights when they
      rise and fall alternately without any considerable change
      of length. See Aurora borealis, under Aurora.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dancer
    n 1: a performer who dances professionally [syn: dancer,
         professional dancer, terpsichorean]
    2: a person who participates in a social gathering arranged for
       dancing (as a ball) [syn: dancer, social dancer]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "dancer":
   artist, artiste, ballerina, ballet dancer, ballet girl,
   ballroom dancer, belly dancer, burlesque queen, choral dancer,
   chorine, chorus boy, chorus girl, clog dancer, conjurer, coryphee,
   dancing girl, danseur, danseur noble, danseuse, ecdysiast,
   entertainer, exotic dancer, female impersonator, figurant,
   figurante, geisha, geisha girl, guisard, guiser,
   heel-and-toe dancer, hoofer, hula girl, impersonator, magician,
   mountebank, mummer, musician, nautch girl, peeler, performer,
   prestidigitator, prima ballerina, public entertainer, show girl,
   singer, square-dancer, stripper, stripteaser, stripteuse,
   terpsichorean, vaudevillian, vaudevillist