The Collaborative International Dictionary of English v.0.48:

Skeptic \Skep"tic\, Skeptical \Skep"tic*al\, a. [Written also
   sceptic, sceptical.]
   1. Of or pertaining to a sceptic or skepticism; characterized
      by skepticism; hesitating to admit the certainly of
      doctrines or principles; doubting of everything.
      [1913 Webster]

   2. (Theol.) Doubting or denying the truth of revelation, or
      the sacred Scriptures.
      [1913 Webster]

            The skeptical system subverts the whole foundation
            of morals.                            --R. Hall.
      [1913 Webster] -- Skep"tac*al*ly, adv. --
      Skep"tic*al*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

skeptical
    adj 1: denying or questioning the tenets of especially a
           religion; "a skeptical approach to the nature of
           miracles" [syn: disbelieving, skeptical, sceptical,
           unbelieving]
    2: marked by or given to doubt; "a skeptical attitude"; "a
       skeptical listener" [syn: doubting, questioning,
       skeptical, sceptical]