The Collaborative International Dictionary of English v.0.48:

parimutuel \par`i*mu"tu*el\ (p[a^]r`[i^]*m[=u]"ch[=oo]*[u^]l),
   n.
   A form of betting where winners share the total amount
   wagered, in proporation to their bets, and less a portion for
   the management; -- used commonly in betting at horse racing
   track. In parimutuel betting, the payoff for a bet does not
   have fixed odds, but depends on the amount bet on each
   outcome.
   [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

parimutuel
    n 1: betting where winners share the total amount wagered