strapless

strapless
    adj 1: having no straps; "a strapless evening gown"
    n 1: a woman's garment that exposes the shoulders and has no
         shoulder straps
    

21 Moby Thesaurus words for "strapless":
      clothesless, decollete, disrobed, en deshabille, garbless,
      garmentless, half-clothed, in dishabille, low-cut, nudish,
      raimentless, topless, unattired, uncased, unclad, unclothed,
      undraped, undressed, ungarbed, ungarmented, unrobed