be ‧ tray /bɪˈtreɪ/ BrE AmE verb [transitive]
[ Date: 1200-1300 ; Origin: tray 'to betray' (13-16 centuries) , from Old French traïr , from Latin tradere ; ⇨ ↑ traitor ]
1 . FRIENDS 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 that someone has trusted me with) .
2 . COUNTRY to be disloyal to your country, company etc, for example by giving secret information to its enemies:
people who betray their country for money
3 . EMOTIONS [not in progressive or passive] to show feelings that you are trying to hide SYN give away :
His voice betrayed his nervousness.
His face betrayed nothing (=showed no emotion) .
4 . TRUTH to show that something is true or exists, especially when it is not easily noticed SYN give away :
The slightest sound might betray his presence.
The crumpled sheets betrayed the fact that someone had been sleeping there.
5 . betray your beliefs/principles/ideals etc to stop supporting your old beliefs and principles, especially in order to get power or avoid trouble
—betrayer noun [countable]