WordNet (r) 3.0 (2006):

fink
    n 1: someone acting as an informer or decoy for the police [syn:
         fink, snitch, snitcher, stoolpigeon, stool
         pigeon, stoolie, sneak, sneaker, canary]
    v 1: take the place of work of someone on strike [syn: fink,
         scab, rat, blackleg]
    2: confess to a punishable or reprehensible deed, usually under
       pressure [syn: confess, squeal, fink]