The Collaborative International Dictionary of English v.0.48:

Underdressed \Un`der*dressed"\, a.
   Not dresses enough.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

clothed \clothed\ adj.
   1. wearing clothing. [Narrower terms: adorned(predicate),
      bedecked(predicate), decked(predicate), decked
      out(predicate); appareled, attired, clad, dressed,
      garbed, garmented, habilimented, robed; arrayed,
      panoplied; breeched, pantalooned, trousered;
      bundled-up; caparisoned; cassocked: costumed:
      decent] [Narrower terms: dight] [Narrower terms:
      dressed-up, dressed to the nines(predicate), dressed to
      kill(predicate), dolled up, spruced up, spiffed up]
      [Narrower terms: gowned] [Narrower terms: habited]
      [Narrower terms: heavy-coated] [Narrower terms:
      overdressed] [Narrower terms: petticoated] [Narrower
      terms: red-coated, lobster-backed] [Narrower terms:
      surpliced] [Narrower terms: togged dressed esp in smart
      clothes)] [Narrower terms: turned out] [Narrower terms:
      underdressed] [Narrower terms: uniformed] [Narrower
      terms: vestmented] Also See: adorned, decorated.
      Antonym: unclothed.
      [WordNet 1.5]

   2. covered with or as if with clothes or a wrap or cloak.
      fog-cloaked meadows

   Syn: cloaked, draped, mantled, wrapped.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

underdressed
    adj 1: inadequately or too informally clothed