The Collaborative International Dictionary of English v.0.48:

Mandate \Man"date\, n. [L. mandatum, fr. mandare to commit to
   one's charge, order, orig., to put into one's hand; manus
   hand + dare to give: cf. F. mandat. See Manual, Date a
   time, and cf. Commend, Maundy Thursday.]
   1. An official or authoritative command, order, or
      authorization from a superior official to a subordinate;
      an order or injunction; a commission; a judicial precept.
      [1913 Webster]

            This dream all-powerful Juno; I bear
            Her mighty mandates, and her words you hear.
                                                  --Dryden.
      [1913 Webster]

   2. Hence: (Politics) An authorization to carry out a specific
      public policy, given by the electorate to their
      representatives; -- it is considered to be implied by the
      election of a candidate by a significant margin after that
      candidate has campaigned with that policy as a prominent
      element of the campaign platform.
      [PJC]

   3. Hence: Authorization by a multinational body to a nation
      to administer the government and affairs of a territory,
      usually a former colony; as, termination of the British
      mandate in Palestine.
      [PJC]

   4. (Canon Law) A rescript of the pope, commanding an ordinary
      collator to put the person therein named in possession of
      the first vacant benefice in his collation.
      [1913 Webster]

   5. (Scots Law) A contract by which one employs another to
      manage any business for him. By the Roman law, it must
      have been gratuitous. --Erskine.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mandate
    n 1: a document giving an official instruction or command [syn:
         mandate, authorization, authorisation]
    2: a territory surrendered by Turkey or Germany after World War
       I and put under the tutelage of some other European power
       until they are able to stand by themselves [syn: mandate,
       mandatory]
    3: the commission that is given to a government and its policies
       through an electoral victory
    v 1: assign under a mandate; "mandate a colony"
    2: make mandatory; "the new director of the school board
       mandated regular tests"
    3: assign authority to