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]

WordNet (r) 3.0 (2006):

patronizingly
    adv 1: with condescension; in a patronizing manner; "he treats
           his secretary condescendingly" [syn: condescendingly,
           patronizingly, patronisingly]