The Collaborative International Dictionary of English v.0.48:

Decorative \Dec"o*ra*tive\ (d[e^]k"[-o]*r[.a]*t[i^]v or
   d[e^]k"[-o]*r[asl]*t[i^]v), a. [Cf. F. d['e]coratif.]
   Suited to decorate or embellish; adorning. --
   Dec"o*ra*tive*ness, n.
   [1913 Webster]

   Decorative art, fine art which has for its end
      ornamentation, rather than the representation of objects
      or events.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decorativeness
    n 1: an appearance that serves to decorate and make something
         more attractive