The Collaborative International Dictionary of English v.0.48:

unconscious \un*con"scious\ ([u^]n*k[o^]n"sh[u^]s), a.
   1. Not conscious; having no consciousness or power of mental
      perception; without cerebral appreciation; hence, not
      knowing or regarding; ignorant; as, an unconscious man.
      --Cowper.
      [1913 Webster]

   2. Not known or apprehended by consciousness; resulting from
      neural activity of which a person is not aware; as, an
      unconscious movement; unconscious cerebration.
      "Unconscious causes." --Blackmore.
      [1913 Webster]

   3. Having no knowledge by experience; -- followed by of; as,
      a mule unconscious of the yoke. --Pope.
      [1913 Webster]

   4. Unintentional; as, an unconscious insult.
      [PJC] -- Un*con"scious*ly, adv. -- Un*con"scious*ness,
      n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unconsciousness
    n 1: a state lacking normal awareness of the self or environment
         [ant: consciousness]