1. 使显得必要(或正当)
    If something warrants a particular action, it makes the action seem necessary or appropriate for the circumstances.

warrant什么意思

    e.g. The allegations are serious enough to warrant an investigation...
           这些指控很严重，有必要进行一番调查。
    e.g. No matter was too small to warrant his attention.
           再小的事也会引起他的注意。

2. 搜查令;拘捕令；令状
    A warrant is a legal document that allows someone to do something, especially one that is signed by a judge or magistrate and gives the police permission to arrest someone or search their house.

    e.g. Police confirmed that they had issued a warrant for his arrest.
           警方证实他们已经签发了对他的拘捕令。
    e.g. ...a search warrant...
           搜查令

3. 正当理由
    If you say that there is no warrant for something, you mean that there is no good reason to justify it.

warrant的翻译

    e.g. There is some warrant for holding back on full-scale aid.
           有理由不进行全面援助。

4. 保证;担保
    If you warrant that something is true or will happen, you say officially that it is true, or guarantee that it will happen.

    e.g. All entrants must warrant that their entry is entirely their own work...
           所有参赛者必须保证其参赛作品完全是自己创作的。
    e.g. The contract warrants that an experienced person is on board all the time.
           合同确保一位富有经验的人会一直呆在船上。

5. see also: death warrant