WordNet (r) 3.0 (2006):

foul play
    n 1: unfair or dishonest behavior (especially involving
         violence)

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "foul play":
   artifice, assassination, blood, bloody murder, bumping-off,
   chicane, chicanery, collusion, connivance, connivery, conspiracy,
   covin, crime, deception, dirty pool, dirty trick, dirty work,
   dodgery, double-dealing, duplicity, elimination, falseheartedness,
   foul, guile, hanky-panky, homicide, killing, liquidation,
   machination, manslaughter, murder, perfidiousness, perfidy,
   pettifoggery, pettifogging, purge, purging, removal,
   sharp practice, skulduggery, sleight, supercherie, thuggee,
   thuggery, thuggism, treacherousness, treachery, trickery,
   underhand dealing, unfairness, unsportsmanlikeness,
   unsportsmanliness