(noun) fink, sneak, sneaker, snitcher, stool pigeon, stoolie, stoolpigeon, canary
someone acting as an informer or decoy for the police
(verb) rat, stag, shit, shop, denounce, betray, tell on, give away, grass
give away information about somebody
He told on his classmate who had cheated on the exam
(verb) thieve, hook, glom, cop, knock off
take by theft
Someone snitched my wallet!