The Collaborative International Dictionary of English v.0.48:

Gamecock \Game"cock`\ (g[=a]m"k[o^]k`), n. (Zool.)
   The male game fowl.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gamecock
    n 1: a cock bred and trained for fighting [syn: gamecock,
         fighting cock]
    2: someone who is a very fierce fighter [syn: hell-kite,
       hell-rooster, gamecock]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "gamecock":
   Achilles, David, Hector, Roland, Samson, a man, battler,
   belligerent, belted knight, bickerer, blade, brave, bravo, brawler,
   bulldog, bully, bullyboy, chutzpanik, combatant, competitor,
   contender, contestant, decorated hero, demigod, demigoddess,
   disputant, duelist, enforcer, fencer, feuder, fighter,
   fighting cock, foilsman, gallant, gladiator, good soldier, goon,
   gorilla, hatchet man, hero, heroine, hood, hoodlum, hooligan,
   jouster, knight, lion, man of courage, militant, paladin,
   plug-ugly, quarreler, rioter, rival, rough, rowdy, ruffian,
   sabreur, scrapper, scuffler, squabbler, stalwart, strong arm,
   strong-arm man, strong-armer, struggler, swashbuckler, sword,
   swordplayer, swordsman, the brave, thug, tiger, tilter, tough,
   tussler, valiant, valiant knight, wrangler