The Collaborative International Dictionary of English v.0.48:

Gambler \Gam"bler\, n.
   One who gambles.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gambler
    n 1: a person who wagers money on the outcome of games or
         sporting events
    2: someone who risks loss or injury in the hope of gain or
       excitement [syn: gambler, risk taker]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "gambler":
   adventurer, betting ring, bettor, boneshaker, cardshark, cardsharp,
   cardsharper, compulsive gambler, crap shooter, gamester, hazarder,
   petty gambler, piker, player, plunger, punter, sharp, sharper,
   sharpie, speculator, sport, sporting man, sportsman, tinhorn,
   tipster, tout, venturer, wagerer