The DICT Development Group

  fink
       n : someone acting as an informer or decoy for the police [syn:
           snitch, snitcher, stoolpigeon, stoolie, sneak,
           sneaker, canary]

  41 Moby Thesaurus words for "fink":
     bear witness against, betray, betrayer, blab, blabber, blabberer,
     blabbermouth, blackleg, blow the whistle, canary, delator,
     inform against, inform on, informer, narc, nark, peach, peacher,
     rat, scab, sell out, snitch, snitch on, snitcher, spy, squeal,
     squealer, stool, stool pigeon, stoolie, strikebreaker, talebearer,
     tattle, tattler, tattletale, tell on, telltale, testify against,
     tipster, turn informer, whistle-blower