The Collaborative International Dictionary of English v.0.48:

Topless \Top"less\, a.
   1. Having no top, or no visble fop; hence, fig.: very lofty;
      supreme; unequaled. " The topless Apennines." "Topless
      fortunes." --Beau. & Fl.
      [1913 Webster]

   2. wearing no clothes above the waist, said especially of
      women.
      [PJC]

   3. featuring entertainment by women wearing no clothes above
      the waist; as, a topless go-go joint.
      [PJC]

WordNet (r) 3.0 (2006):

topless
    adj 1: having no top; "a topless jar" [ant: topped]
    2: having the breasts uncovered or featuring such nudity;
       "topless waitresses"; "a topless cabaret" [syn: bare-
       breasted, braless, topless]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "topless":
   Olympian, aerial, airy, altitudinous, ascending, aspiring,
   bare-ankled, bare-armed, bare-backed, bare-breasted, bare-chested,
   bare-handed, bare-headed, bare-legged, bare-necked, clothesless,
   colossal, crownless, decollete, disrobed, dominating, elevated,
   eminent, en deshabille, ethereal, exalted, garbless, garmentless,
   half-clothed, haughty, headless, high, high-pitched, high-reaching,
   high-set, high-up, in dishabille, lofty, low-cut, monumental,
   mounting, nudish, outtopping, overlooking, overtopping, prominent,
   raimentless, skyscraping, soaring, spiring, steep, strapless,
   sublime, superlative, supernal, toplofty, topping, towering,
   towery, unattired, uncased, unclad, unclothed, undraped, undressed,
   ungarbed, ungarmented, unrobed, uplifted, upreared