to deliver or expose to an enemy by treachery or disloyalty

Benedict Arnold betrayed his country.

to be unfaithful in guarding, maintaining, or fulfilling

to betray a trust.

to disappoint the hopes or expectations of; be disloyal to

to betray one's friends.

to reveal or disclose in violation of confidence

to betray a secret.

to reveal unconsciously (something one would preferably conceal)

Her nervousness betrays her insecurity.

to show or exhibit; reveal; disclose

an unfeeling remark that betrays his lack of concern.

to deceive, misguide, or corrupt

a young lawyer betrayed by political ambitions into irreparable folly.

to seduce and desert.

noun

deceiver , traitor , double-crosser , benedict arnold , backstabber , fink , nark , narc , snitch , turncoat , spy , stool pigeon * , weasel , rat , judas , informer , seducer , skunk , stoolie