The Collaborative International Dictionary of English v.0.48:

Welsher \Welsh"er\, n.
   One who cheats at a horse race; one who bets, without a
   chance of being able to pay; one who receives money to back
   certain horses and absconds with it. [Written also
   welcher.] [Slang, Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

welsher
    n 1: someone who swindles you by not repaying a debt or wager
         [syn: welcher, welsher]