WordNet (r) 3.0 (2006):

snitch
    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 by theft; "Someone snitched my wallet!" [syn: hook,
         snitch, thieve, cop, knock off, glom]
    2: give away information about somebody; "He told on his
       classmate who had cheated on the exam" [syn: denounce,
       tell on, betray, give away, rat, grass, shit,
       shop, snitch, stag]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "snitch":
   abstract, and, annex, appropriate, bag, beak, bear witness against,
   beezer, betray, betrayer, blab, blabber, blabberer, blabbermouth,
   blow the whistle, boost, borrow, canary, conk, cop, crib, defraud,
   delator, embezzle, extort, filch, fink, hook, inform against,
   inform on, informer, lift, make off with, narc, nark, nick, nip,
   palm, peach, peacher, pecker, pilfer, pimp, pinch, poach, purloin,
   rat, run away with, rustle, schnozzle, scrounge, sell out,
   shoplift, sing, smeller, snare, snatch, snitch on, snitcher, snout,
   spy, squeak, squeal, squealer, steal, stool, stool pigeon, stoolie,
   swindle, swipe, take, talebearer, tattle, tattler, tattletale,
   tell on, telltale, testify against, thieve, tipster, turn informer,
   walk off with, whistle-blower