Source : Webster's Revised Unabridged Dictionary (1913)

Apparition \Ap`pa*ri"tion\, n. [F. apparition, L. apparitio, fr.
   apparere. See {Appear}.]
   1. The act of becoming visible; appearance; visibility.
      --Milton.

            The sudden apparition of the Spaniards. --Prescott.

            The apparition of Lawyer Clippurse occasioned much
            speculation in that portion of the world. --Sir W.
                                                  Scott.

   2. The thing appearing; a visible object; a form.

            Which apparition, it seems, was you.  --Tatler.

   3. An unexpected, wonderful, or preternatural appearance; a
      ghost; a specter; a phantom. ``The heavenly bands . . . a
      glorious apparition.'' --Milton.

            I think it is the weakness of mine eyes That shapes
            this monstrous apparition.            --Shak.

   4. (Astron.) The first appearance of a star or other luminary
      after having been invisible or obscured; -- opposed to
      {occultation}.

   {Circle of perpetual apparition}. See under {Circle}.

Source : WordNet®

apparition
     n 1: a ghostly appearing figure; "we were unprepared for the
          apparition that confronted us" [syn: {phantom}, {phantasm},
           {phantasma}, {specter}, {spectre}]
     2: the appearance of a ghostlike figure; "I was recalled to the
        present by the apparition of a frightening specter"
     3: something existing in perception only; "a ghostly apparition
        at midnight" [syn: {phantom}, {phantasm}, {phantasma}, {shadow}]
     4: an act of appearing or becoming visible unexpectedly;
        "natives were amazed at the apparition of this white
        stanger"