Other forms: betrayed, betraying, betrays
To betray somebody is to turn against them after they trusted you. Betray a friend, betray a country, feel betrayed.
It also means to reveal something you should have kept hidden — betray a secret — and, more subtly, to show a feeling without meaning to: her voice betrayed nothing, his face betrayed him. That third sense is common in fiction and is worth recognising because it needs no villain. The noun is betrayal, and a traitor is the person, though betrayer exists. Note that betray takes a direct object always: betray somebody, never betray to somebody.
1verbbetrayTo act against somebody who trusted you.
“He betrayed everybody who had helped him.”
synonyms: double-cross, sell out
2verbrevealTo reveal a secret.
“She never betrayed where the money had come from.”
3verbshowTo show a feeling without meaning to.
“His face betrayed nothing at all.”
Too few real examples of this word to estimate which sense is commonest.
betray is a breaking of trust.
Betray is be- plus the Old French trair, to hand over, from Latin tradere — the same verb behind tradition and traitor. Handing something on and handing somebody over are the same word, which is an uncomfortable thought and a true etymology.
Proto-Germanic
*bi- — be-
Old English
be- — be-
Middle English
betrayen
English, today
betray
Built from
From Middle English betrayen, bitrayen (“to commit an act of treason against”), equivalent to be- + tray. bi- is from Old English be- (“be-”), from Proto-Germanic bi- (“be-”), from Proto-Germanic bi (“near, by”), ultimately from Proto-Indo-European h₁epi (“at, near”). Compare also traitor, treason, tradition. The modern sense to disclose, discover, reveal unintentionally is due to influence from or merger with English bewray (“to reveal, divulge”), which is similar in sound and meaning. The similarity with German betrügen, Dutch bedriegen, from Proto-West Germanic bidreugan (“to betray, deceive”), is coincidental.
Etymology from Wiktionary, CC BY-SA