Source : Webster's Revised Unabridged Dictionary (1913)

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["a]hren;
   akin to OFries. wera. Cf. {Guarantee}.]
   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:
      (a) A writing which authorizes a person to receive money
          or other thing.
      (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.
      (c) (Mil. & Nav.) An official certificate of appointment
          issued to an officer of lower rank than a commissioned
          officer. See {Warrant officer}, below.

   2. That which vouches or insures for anything; guaranty;
      security.

            I give thee warrant of thy place.     --Shak.

            His worth is warrant for his welcome hither. --Shak.

   3. That which attests or proves; a voucher.

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

   {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.

Warrant \War"rant\, v. t. [imp. & p. p. {Warranted}; p. pr. &
   vb. n. {Warranting}.] [OE. waranten, OF. warantir, garantir,
   guarantir, garentir, garandir, F. garantir to warrant, fr.
   OF. warant, garant, guarant, a warrant, a protector, a
   defender, F. garant. [root]142. See {Warrant}, n.]
   1. To make secure; to give assurance against harm; to
      guarantee safety to; to give authority or power to do, or
      forbear to do, anything by which the person authorized is
      secured, or saved harmless, from any loss or damage by his
      action.

            That show I first my body to warrant. --Chaucer.

            I'll warrant him from drowning.       --Shak.

            In a place Less warranted than this, or less secure,
            I can not be.                         --Milton.

   2. To support by authority or proof; to justify; to maintain;
      to sanction; as, reason warrants it.

            True fortitude is seen in great exploits, That
            justice warrants, and that wisdom guides. --Addison.

            How little while it is since he went forth out of
            his study, -- chewing a Hebrew text of Scripture in
            his mouth, I warrant.                 --Hawthorne.

   3. To give a warrant or warranty to; to assure as if by
      giving a warrant to.

            [My neck is] as smooth as silk, I warrant ye. --L'
                                                  Estrange.

   4. (Law)
      (a) To secure to, as a grantee, an estate granted; to
          assure.
      (b) To secure to, as a purchaser of goods, the title to
          the same; to indemnify against loss.
      (c) To secure to, as a purchaser, the quality or quantity
          of the goods sold, as represented. See {Warranty}, n.,
          2.
      (d) To assure, as a thing sold, to the purchaser; that is,
          to engage that the thing is what it appears, or is
          represented, to be, which implies a covenant to make
          good any defect or loss incurred by it.

Source : WordNet®

warrant
     n 1: a writ from a court commanding police to perform specified
          acts
     2: a type of security issued by a corporation (usually together
        with a bond or preferred stock) that gives the holder the
        right to purchase a certain amount of common stock at a
        stated price; "as a sweetener they offered warrants along
        with the fixed-income securities" [syn: {stock warrant}, {stock-purchase
        warrant}]
     3: formal and explicit approval; "a Democrat usually gets the
        union's endorsement" [syn: {sanction}, {countenance}, {endorsement},
         {indorsement}, {imprimatur}]
     4: a written assurance that some product or service will be
        provided or will meet certain specifications [syn: {guarantee},
         {warrantee}, {warranty}]

warrant
     v 1: show to be reasonable or provide adequate ground for; "The
          emergency does not warrant all of us buying guns"; "The
          end justifies the means" [syn: {justify}]
     2: stand behind and guarantee the quality, accuracy, or
        condition of; "The dealer warrants all the cars he sells";
        "I warrant this information" [syn: {guarantee}]