The Collaborative International Dictionary of English v.0.48:

District \Dis"trict\, n. [LL. districtus district, fr. L.
   districtus, p. p. of distringere: cf. F. district. See
   Distrain.]
   1. (Feudal Law) The territory within which the lord has the
      power of coercing and punishing.
      [1913 Webster]

   2. A division of territory; a defined portion of a state,
      town, or city, etc., made for administrative, electoral,
      or other purposes; as, a congressional district, judicial
      district, land district, school district, etc.
      [1913 Webster]

            To exercise exclusive legislation . . . over such
            district not exceeding ten miles square. --The
                                                  Constitution
                                                  of the United
                                                  States.
      [1913 Webster]

   3. Any portion of territory of undefined extent; a region; a
      country; a tract.
      [1913 Webster]

            These districts which between the tropics lie.
                                                  --Blackstone.
      [1913 Webster]

   Congressional district. See under Congressional.

   District attorney, the prosecuting officer of a district or
      district court.

   District court, a subordinate municipal, state, or United
      States tribunal, having jurisdiction in certain cases
      within a judicial district.

   District judge, one who presides over a district court.

   District school, a public school for the children within a
      school district. [U.S.]

   Syn: Division; circuit; quarter; province; tract; region;
        country.
        [1913 Webster]

WordNet (r) 3.0 (2006):

district attorney
    n 1: an official prosecutor for a judicial district [syn:
         district attorney, DA]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "district attorney":
   AG, DA, KC, QC, SSC, US attorney, attorney general, civilian,
   corporation lawyer, court-appointed lawyer, criminal lawyer,
   defense counsel, junior counsel, law agent, leader, mouthpiece,
   private attorney, prosecuting attorney, prosecutor,
   public prosecutor, publicist, silk, silk gown, solicitor general,
   special pleader, stuff gown, stuff-gownsman