The Collaborative International Dictionary of English v.0.48:

Aristocrat \A*ris"to*crat\ (?; 277), n. [F. aristocrate. See
   Aristocracy.]
   1. One of the aristocracy or people of rank in a community;
      one of a ruling class; a noble.
      [1913 Webster]

   2. One who is overbearing in his temper or habits; a proud or
      haughty person.
      [1913 Webster]

            A born aristocrat, bred radical.      --Mrs.
                                                  Browning.
      [1913 Webster]

   3. One who favors an aristocracy as a form of government, or
      believes the aristocracy should govern.
      [1913 Webster]

            His whole family are accused of being aristocrats.
                                                  --Romilly.
      [1913 Webster] Aristocratic

WordNet (r) 3.0 (2006):

aristocrat
    n 1: a member of the aristocracy [syn: aristocrat, blue
         blood, patrician]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "aristocrat":
   Brahman, archduke, armiger, baron, baronet, blue blood, count,
   daimio, duke, earl, esquire, gentleman, grand duke, grandee,
   hidalgo, lace-curtain, laird, landgrave, lord, lordling, magnate,
   magnifico, margrave, marquis, noble, nobleman, optimate, palsgrave,
   patrician, peer, seigneur, seignior, silk-stocking, squire, swell,
   thoroughbred, upper-cruster, viscount, waldgrave