/ bɪˈtreɪ; NAmE / verb [ vn ]
1.
betray sb/sth (to sb) to give information about sb/sth to an enemy :
For years they had been betraying state secrets to Russia.
He was offered money to betray his colleagues.
2.
to hurt sb who trusts you, especially by not being loyal or faithful to them :
She felt betrayed when she found out the truth about him.
She betrayed his trust over and over again.
I have never known her to betray a confidence (= tell other people sth that should be kept secret) .
➡ note at cheat
3.
to ignore your principles or beliefs in order to achieve sth or gain an advantage for yourself :
He has been accused of betraying his former socialist ideals.
4.
betray sth / yourself to tell sb or make them aware of a piece of information, a feeling, etc., usually without meaning to
SYN give away :
His voice betrayed the worry he was trying to hide.
She was terrified of saying something that would make her betray herself (= show her feelings or who she was) .
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WORD ORIGIN
Middle English : from be- thoroughly + obsolete tray betray , from Old French trair , based on Latin tradere hand over.