The Collaborative International Dictionary of English v.0.48:

Contestant \Con*test"ant\, n. [Cf. F. contestant.]
   One who contests; an opponent; a litigant; a disputant; one
   who claims that which has been awarded to another.
   [1913 Webster]

WordNet (r) 3.0 (2006):

contestant
    n 1: a person who participates in competitions
    2: a person who dissents from some established policy [syn:
       dissenter, dissident, protester, objector,
       contestant]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "contestant":
   adversary, battler, belligerent, belted knight, bickerer, blade,
   bravo, brawler, bully, bullyboy, carouser, combatant, competitor,
   contender, corrival, cutup, disputant, duelist, emulator, enforcer,
   entrant, fencer, feuder, fighter, fighting cock, foilsman, frisker,
   frolicker, funmaker, gamboler, gamecock, gladiator, goon, gorilla,
   hatchet man, hood, hoodlum, hooligan, jouster, knight, merrymaker,
   militant, opponent, participant, playboy, player, pleasure-seeker,
   pleasurer, pleasurist, plug-ugly, quarreler, reveler, rioter,
   rival, rollicker, rough, rowdy, ruffian, sabreur, scrapper,
   scuffler, skylarker, squabbler, strong arm, strong-arm man,
   strong-armer, struggler, swashbuckler, sword, swordplayer,
   swordsman, the field, thug, tilter, tough, tussler, vier,
   wrangler