If something warrants a particular action, it makes the action seem necessary or appropriate for the circumstances.

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.

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

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