Source : Webster's Revised Unabridged Dictionary (1913)

Commissioner \Com*mis"sion*er\, n.
   1. A person who has a commission or warrant to perform some
      office, or execute some business, for the government,
      corporation, or person employing him; as, a commissioner
      to take affidavits or to adjust claims.

            To another address which requested that a commission
            might be sent to examine into the state of things in
            Ireland, William returned a gracious answer, and
            desired the Commons to name the commissioners.
                                                  --Macaulay.

   2. An officer having charge of some department or bureau of
      the public service.

            Herbert was first commissioner of the Admiralty.
                                                  --Macaulay.

            The commissioner of patents, the commissioner of the
            land office, the commissioner of Indian affairs, are
            subordinates of the secretary of the interior.
                                                  --Bartlett.

   {Commissioner of deeds}, an officer having authority to take
      affidavits, depositions, acknowledgment of deeds, etc.,
      for use in the State by which he is appointed. [U. S.]

   {County commissioners}, certain administrative officers in
      some of the States, invested by local laws with various
      powers in reference to the roads, courthouses, financial
      matters, etc., of the county. [U. S.]

Source : WordNet®

commissioner
     n 1: a government administrator
     2: a member of a commission