|Origin:||tray 'to betray' (13-16 centuries), from Old French traïr, from Latin tradere; TRAITOR|
to be disloyal to someone who trusts you so that they are harmed or upset:
He felt that she had betrayed him.
betray somebody to somebody
What kind of man would betray his own sister to the police?
She had betrayed her parents' trust.
I would never betray a confidence (=tell a secret which someone has trusted me with).
to be disloyal to your country, company etc, for example by giving secret information to its enemies:
people who betray their country for money
to show feelings that you are trying to hide [= give away]:
emotions[not in progressive or passive]
His voice betrayed his nervousness.
His face betrayed nothing (=showed no emotion).
to show that something is true or exists, especially when it is not easily noticed [= give away]:
The slightest sound might betray his presence.
The crumpled sheets betrayed the fact that someone had been sleeping there.
to stop supporting your old beliefs and principles, especially in order to get power or avoid trouble
—betrayer noun [countable]