The Collaborative International Dictionary of English v.0.48:

Warrant \War"rant\, n. [OE. warant, OF. warant a warrant, a
   defender, protector, F. garant, originally a p. pr. pf German
   origin, fr. OHG. wer[=e]n to grant, warrant, G. gew[aum]hren;
   akin to OFries. wera. Cf. Guarantee.]
   [1913 Webster]
   1. That which warrants or authorizes; a commission giving
      authority, or justifying the doing of anything; an act,
      instrument, or obligation, by which one person authorizes
      another to do something which he has not otherwise a right
      to do; an act or instrument investing one with a right or
      authority, and thus securing him from loss or damage;
      commission; authority. Specifically:
      [1913 Webster]
      (a) A writing which authorizes a person to receive money
          or other thing.
          [1913 Webster]
      (b) (Law) A precept issued by a magistrate authorizing an
          officer to make an arrest, a seizure, or a search, or
          do other acts incident to the administration of
          justice.
          [1913 Webster]
      (c) (Mil. & Nav.) An official certificate of appointment
          issued to an officer of lower rank than a commissioned
          officer. See Warrant officer, below.
          [1913 Webster]

   2. That which vouches or insures for anything; guaranty;
      security.
      [1913 Webster]

            I give thee warrant of thy place.     --Shak.
      [1913 Webster]

            His worth is warrant for his welcome hither. --Shak.
      [1913 Webster]

   3. That which attests or proves; a voucher.
      [1913 Webster]

   4. Right; legality; allowance. [Obs.] --Shak.
      [1913 Webster]

   Bench warrant. (Law) See in the Vocabulary.

   Dock warrant (Com.), a customhouse license or authority.

   General warrant. (Law) See under General.

   Land warrant. See under Land.

   Search warrant. (Law) See under Search, n.

   Warrant of attorney (Law), written authority given by one
      person to another empowering him to transact business for
      him; specifically, written authority given by a client to
      his attorney to appear for him in court, and to suffer
      judgment to pass against him by confession in favor of
      some specified person. --Bouvier.

   Warrant officer, a noncommissioned officer, as a sergeant,
      corporal, bandmaster, etc., in the army, or a
      quartermaster, gunner, boatswain, etc., in the navy.

   Warrant to sue and defend.
      (a) (O. Eng. Law) A special warrant from the crown,
          authorizing a party to appoint an attorney to sue or
          defend for him.
      (b) A special authority given by a party to his attorney
          to commence a suit, or to appear and defend a suit in
          his behalf. This warrant is now disused. --Burrill.
          [1913 Webster]

WordNet (r) 3.0 (2006):

warrant officer
    n 1: holds rank by virtue of a warrant

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "warrant officer":
   NCO, acting corporal, acting sergeant, admiral, captain, centurion,
   chief petty officer, chief warrant officer, color sergeant,
   commander, commodore, corporal, ensign, first sergeant,
   fleet admiral, havildar, lance corporal, lance sergeant,
   lieutenant, lieutenant commander, lieutenant junior grade,
   master sergeant, mess sergeant, naik, naval officer, navarch,
   noncom, noncommissioned officer, petty officer, platoon sergeant,
   rear admiral, sarge, sergeant, sergeant first class,
   sergeant major, skipper, staff sergeant, technical sergeant,
   top sergeant, topkick, vice admiral