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