Source : Webster's Revised Unabridged Dictionary (1913)

Specter \Spec"ter\, Spectre \Spec"tre\, n. [F. spectre, fr. L.
   spectrum an appearance, image, specter, fr. specere to look.
   See {Spy}, and cf. {Spectrum}.]
   1. Something preternaturally visible; an apparition; a ghost;
      a phantom.

            The ghosts of traitors from the bridge descend, With
            bold fanatic specters to rejoice.     --Dryden.

   2. (Zo["o]l.)
      (a) The tarsius.
      (b) A stick insect.

   {Specter bat} (Zo["o]l.), any phyllostome bat.

   {Specter candle} (Zo["o]l.), a belemnite.

   {Specter shrimp} (Zo["o]l.), a skeleton shrimp. See under
      {Skeleton}.

Source : WordNet®

specter
     n 1: a mental representation of some haunting experience; "he
          looked like he had seen a ghost"; "it aroused specters
          from his past" [syn: {ghost}, {shade}, {spook}, {wraith},
           {spectre}]
     2: a ghostly appearing figure; "we were unprepared for the
        apparition that confronted us" [syn: {apparition}, {phantom},
         {phantasm}, {phantasma}, {spectre}]