The Collaborative International Dictionary of English v.0.48:

Patronizing \Pa"tron*i`zing\, a.
   Showing condescending favor; assuming the manner of airs of a
   superior toward another. -- Pat"ron*i`zing*ly, adv.
   --Thackeray.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Patronize \Pa"tron*ize\, v. t. [imp. & p. p. Patronized; p.
   pr. & vb. n. Patronizing.]
   1. To act as patron toward; to support; to countenance; to
      favor; to aid.
      [1913 Webster]

            The idea has been patronized by two States only.
                                                  --A. Hamilton.
      [1913 Webster]

   2. To trade with customarily; to frequent as a customer.
      [Commercial Cant]
      [1913 Webster]

   3. To assume the air of a patron, or of a superior and
      protector, toward; -- used in an unfavorable sense; as, to
      patronize one's equals.
      [1913 Webster]

WordNet (r) 3.0 (2006):

patronizing
    adj 1: (used of behavior or attitude) characteristic of those
           who treat others with condescension [syn: arch,
           condescending, patronizing, patronising]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "patronizing":
   Olympian detachment, Olympian loftiness, arrogance, arrogant,
   arrogantness, assumption of superiority, big, condescendence,
   condescending, condescension, domineering, domineeringness,
   haughtiness, haughty, haughty airs, hauteur, high horse,
   high-faluting, high-flown, high-hat, high-headed, high-nosed,
   hoity-toitiness, hoity-toity, loftiness, lofty, overbearing,
   overbearing pride, overbearingness, overweening pride,
   patronization, patronizing attitude, pride, priggish, proud,
   proudness, purse-pride, purse-proud, side, sniffy, snippy,
   snobbish, snobby, snooty, snotty, stiff-necked pride, stuck-up,
   superbia, superior, toploftiness, toplofty, uppish, uppishness,
   uppity, uppityness, upstage