SYNONYMS
break one's promise to, be disloyal to, be unfaithful to, break faith with, play someone false, fail, let down
double-cross, deceive, cheat
inform against, inform on, give away, denounce, sell out, stab someone in the back, be a Judas to, give someone a Judas kiss, bite the hand that feeds one
turn traitor, sell the pass
turn King's evidence, turn Queen's evidence
informal blow the whistle on, rat on, peach on, sell down the river, squeal on, squeak on
British informal grass on, shop, sneak on, stitch up, do the dirty on, split on
North American informal rat out, drop a dime on, drop the dime on, finger, job
Australian, New Zealand informal dob on, pimp on, pool, shelf, put someone's pot on, point the bone at
rare delate