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]