Warrant  —n. 1 thing that authorizes an action. 2 a written authorization, money voucher, etc. B written authorization allowing police to search premises, arrest a suspect, etc. 3 certificate of service rank held by a warrant-officer. —v. 1 serve as a warrant for; justify. 2 guarantee or attest to esp. The genuineness of.  i (or i'll) warrant i am certain; no doubt. [french warant, from germanic]