The Collaborative International Dictionary of English v.0.48:

Demeanor \De*mean"or\, n. [Written also demeanour.] [For
   demeanure, fr. demean. See Demean, v. t.]
   1. Management; treatment; conduct. [Obs.]
      [1913 Webster]

            God commits the managing so great a trust . . .
            wholly to the demeanor of every grown man. --Milton.
      [1913 Webster]

   2. Behavior; deportment; carriage; bearing; mien.
      [1913 Webster]

            His demeanor was singularly pleasing. --Macaulay.
      [1913 Webster]

            The men, as usual, liked her artless kindness and
            simple refined demeanor.              --Thackeray.
      [1913 Webster]

WordNet (r) 3.0 (2006):

demeanour
    n 1: (behavioral attributes) the way a person behaves toward
         other people [syn: demeanor, demeanour, behavior,
         behaviour, conduct, deportment]