1. 失信于；辜负
    If you betray someone who loves or trusts you, your actions hurt and disappoint them.

    e.g. When I tell someone I will not betray his confidence I keep my word...
           如果我告诉某人我不会辜负他的信任，我就会恪守诺言。
    e.g. The President betrayed them when he went back on his promise not to raise taxes.
           总统背叛了他们，违背了不加税的诺言。

2. 背叛；出卖
    If someone betrays their country or their friends, they give information to an enemy, putting their country's security or their friends' safety at risk.

    e.g. They offered me money if I would betray my associates...
           他们提出来只要我供出同伙就给我钱。
    e.g. The group were informers, and they betrayed the plan to the Germans.
           这帮人是告密者，他们把计划泄露给了德国人。

3. 违背，背弃（理想或原则）
    If you betray an ideal or your principles, you say or do something which goes against those beliefs.

    e.g. We betray the ideals of our country when we support capital punishment.
           如果我们支持死刑，那就背弃了我们立国的理念。

4. 流露出；暴露出
    If you betray a feeling or quality, you show it without intending to.

betray的意思

    e.g. She studied his face, but it betrayed nothing...
           她仔细端详了一番他的脸，但什么也没有看出来。
    e.g. He nodded his head instead of saying anything where his voice might betray him.
           他一言不发，只是点头，因为一开口可能会露出破绽。