The Collaborative International Dictionary of English v.0.48:

Sweepstakes \Sweep"stakes`\, n.
   1. A winning of all the stakes or prizes; a sweepstake.
      [1913 Webster]

   2. sing. or pl. The whole money or other things staked at a
      horse race, a given sum being put up for each horse, all
      of which goes to the winner, or is divided among several,
      as may be previously agreed.
      [1913 Webster]

   3. A race for all the sums staked or prizes offered.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sweepstakes
    n 1: a lottery in which the prize consists of the money paid by
         the participants

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "sweepstakes":
   Academy Award, Derby, Kentucky Derby, Nobel Prize, Oscar,
   Preakness Stakes, award, betting system, bingo, booby prize,
   card games, chase, chuck and toss, chuck farthing, chuck-a-luck,
   class lottery, consolation prize, crack-loo, crap game,
   crap shooting, craps, daily double, double-or-nothing,
   draft lottery, drawing, exacta, fan-tan, first prize, flat race,
   grab bag, handicap, handicap race, harness race, hazard,
   horse race, horse racing, hurdle race, interest lottery, jackpot,
   keno, lottery, lotto, martingale, number lottery, numbers pool,
   pari-mutuel, perfecta, pinball, pitch and toss, plate race, policy,
   prize, purse race, quarter-horse race, quinella, raffle, reward,
   rouge et noir, roulette, second prize, shell game, stake,
   stake race, steeplechase, superfecta, sweep, sweeps, sweepstake,
   the numbers, the numbers game, tombola, tontine,
   trente-et-quarante, trotting race