Warrant means to justify or provide grounds for.
Warrant is a verb.
Synonyms: justify, licence, authorize.
Antonyms: negate, invalidate, void.
Note: Warrant can also be a noun meaning a guarantee, authorization, or justification. A written guarantee is called a warranty.
I know it looks old, but the shopkeeper warrants that all the parts are brand new.
The officers have a search warrant.
Will you warrant that the money will be paid on time?