Quick definitions from WordNet (betray)
▸ verb: deliver to an enemy by treachery ("The spy betrayed his country")
▸ verb: reveal unintentionally ("Her smile betrayed her true feelings")
▸ verb: cause someone to believe an untruth
▸ verb: disappoint, prove undependable to; abandon, forsake
▸ verb: give away information about somebody
▸ verb: be sexually unfaithful to one's partner in marriage
▸ Also see betray
▸ verb: deliver to an enemy by treachery ("The spy betrayed his country")
▸ verb: reveal unintentionally ("Her smile betrayed her true feelings")
▸ verb: cause someone to believe an untruth
▸ verb: disappoint, prove undependable to; abandon, forsake
▸ verb: give away information about somebody
▸ verb: be sexually unfaithful to one's partner in marriage
▸ Also see betray