The Collaborative International Dictionary of English v.0.48:

decoration \dec`o*ra"tion\ (d[e^]k`[-o]*r[=a]"sh[u^]n), n. [LL.
   decoratio: cf. F. d['e]coration.]
   1. The act of adorning, embellishing, or honoring;
      ornamentation.
      [1913 Webster]

   2. That which adorns, enriches, or beautifies; something
      added by way of embellishment; ornament.
      [1913 Webster]

            The hall was celebrated for . . . the richness of
            its decoration.                       --Motley.
      [1913 Webster]

   3. Specifically, any mark of honor to be worn upon the
      person, as a medal, cross, or ribbon of an order of
      knighthood, bestowed for services in war, great
      achievements in literature, art, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decoration
    n 1: something used to beautify [syn: decoration, ornament,
         ornamentation]
    2: an award for winning a championship or commemorating some
       other event [syn: decoration, laurel wreath, medal,
       medallion, palm, ribbon]
    3: the act of decorating something (in the hope of making it
       more attractive)