Betrayal

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.
Contemporary Examples

Sex With Madoff Burt Ross August 23, 2009
Hunting the Obama Haters John Avlon December 4, 2008
Super Bowl Lineup: The Best NFL Longreads This Season Ben Teitelbaum January 30, 2014
Baudelaire’s Femme Fatale Muse James MacManus May 6, 2013
The Best-Reviewed Movie of the Year The Daily Beast September 25, 2010

Historical Examples

Wilderness of Spring Edgar Pangborn
The Man Shakespeare Frank Harris
The Vision Spendid William MacLeod Raine
Murder Point Coningsby Dawson
Man and Wife Wilkie Collins

verb (transitive)
to aid an enemy of (one’s nation, friend, etc); be a traitor to: to betray one’s country
to hand over or expose (one’s nation, friend, etc) treacherously to an enemy
to disclose (a secret, confidence, etc) treacherously
to break (a promise) or be disloyal to (a person’s trust)
to disappoint the expectations of; fail: his tired legs betrayed him
to show signs of; indicate: if one taps china, the sound betrays any faults
to reveal unintentionally: his grin betrayed his satisfaction
betray oneself, to reveal one’s true character, intentions, etc
to lead astray; deceive
(euphemistic) to seduce and then forsake (a woman)
n.
v.