The Collaborative International Dictionary of English v.0.48:

Undecorated \Undecorated\
   See decorated.

WordNet (r) 3.0 (2006):

undecorated
    adj 1: not decorated with something to increase its beauty or
           distinction [syn: unadorned, undecorated] [ant:
           adorned, decorated]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "undecorated":
   bald, bare, blank, homely, naked, nude, simple, unadorned,
   unadulterated, unarrayed, uncomplicated, undecked, undressed,
   unembellished, unfurbished, ungarnished, unornamented,
   unsophisticated, untrimmed, unvarnished