The Collaborative International Dictionary of English v.0.48:

Democrat \Dem"o*crat\ (d[e^]m"[-o]*kr[a^]t), n. [Cf. F.
   d['e]mocrate.]
   1. One who is an adherent or advocate of democracy, or
      government by the people.
      [1913 Webster]

            Whatever they call him, what care I,
            Aristocrat, democrat, autocrat.       --Tennyson.
      [1913 Webster]

   2. [capitalized] A member of the Democratic party. [U.S.]
      [1913 Webster]

   3. A large light uncovered wagon with two or more seats. [U.
      S.]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Democrat
    n 1: a member of the Democratic Party
    2: an advocate of democratic principles [syn: democrat,
       populist]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "Democrat":
   Conservative, Labourite, Republican, Tory, Whig, heeler, loyalist,
   partisan, party faithful, party hack, party man, party member,
   party wheelhorse, registered Democrat, registered Republican,
   regular, stalwart, ward heeler, wheelhorse