The Collaborative International Dictionary of English v.0.48:

Undressed \Undressed\
   See dressed.

WordNet (r) 3.0 (2006):

undressed
    adj 1: of lumber or stone or hides; not finished or dressed;
           "undressed granite"; "undressed hides"
    2: having removed clothing [syn: unappareled, unattired,
       unclad, undressed, ungarbed, ungarmented]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "undressed":
   bald, bare, blank, clothesless, crude, decollete, disrobed,
   en deshabille, garbless, garmentless, half-clothed, in dishabille,
   low-cut, naked, nude, nudish, raimentless, raw, rough, roughhewn,
   rude, stark-naked, strapless, stripped, topless, unadorned,
   unadulterated, unarrayed, unattired, uncased, unclad, unclothed,
   uncomplicated, undecked, undecorated, undraped, unembellished,
   unfashioned, unfinished, unformed, unfurbished, ungarbed,
   ungarmented, ungarnished, unhewn, unornamented, unpolished,
   unrobed, unsophisticated, untrimmed, unvarnished, unworked