WordDictionary

Noun:

• A certificate of appointment given to a warrant officer.
• An order that serves as authorization, especially: A voucher authorizing payment or receipt of money.
• Authorization or certification; sanction, as given by a superior.
• A warrant officer.
• NZ A Warrant of Fitness; a document certifying that a motor vehicle meets certain standards of safety and mechanical soundness.
• finance An option, usually with a term at issue greater than a year, usually issued together with another security, to buy other securities of the issuer.
• legal A judicial writ authorizing an officer to make a search, seizure, or arrest or to execute a judgment.
• obsolete A protector or defender.
• Something that provides assurance or confirmation; a guarantee or proof: a warrant of authenticity; a warrant for success.

Verb:

• transitive To give (someone) a guarantee or assurance (of something); also, with double object, to guarantee (someone something).
• transitive To protect, keep safe (from danger).
• transitive To authorize; to give (someone) warrant or sanction (to do something).
• colloquially to believe strongly.
• transitive To guarantee (something) to be (of a specified quality, value etc.).
• transitive To justify; to give grounds for.