to not be loyal to your country or a person, often by doing something harmful such as helping their enemies

He was accused of betraying his country during the war. 他被指控在战争期间背叛了祖国。

She felt betrayed by her mother's lack of support. 她觉得母亲背弃了她，因为母亲没有支持她。

For years they betrayed the UK's secrets to Russia. 他们多年向俄国出卖英国的机密情报。

formal He promised never to betray his wife (= never to leave her for another person). 他承诺永不抛弃自己的妻子。

If someone betrays something such as a promise, they do not do what they promised.

The president has been accused of betraying his election promises. 总统因未能履行竞选诺言而遭到人们的谴责。

By staying out so late, they have betrayed my trust (= disappointed me because I had trusted them not to). 他们在外面呆到这么晚才回来，真是辜负了我的信任。

to show feelings, thoughts, or a particular characteristic without intending to

If he is nervous on stage, he does not betray it. 他即使在舞台上十分紧张，也不会表露出来。

Although she often seems quite cold, her smiling eyes betray her true nature. 虽然看上去总是很冷漠，但她微笑的双眼却显示出了真性情。