Source : Webster's Revised Unabridged Dictionary (1913)

Ghost \Ghost\, n. [OE. gast, gost, soul, spirit, AS. g[=a]st
   breath, spirit, soul; akin to OS. g?st spirit, soul, D.
   geest, G. geist, and prob. to E. gaze, ghastly.]
   1. The spirit; the soul of man. [Obs.]

            Then gives her grieved ghost thus to lament.
                                                  --Spenser.

   2. The disembodied soul; the soul or spirit of a deceased
      person; a spirit appearing after death; an apparition; a
      specter.

            The mighty ghosts of our great Harrys rose. --Shak.

            I thought that I had died in sleep, And was a
            blessed ghost.                        --Coleridge.

   3. Any faint shadowy semblance; an unsubstantial image; a
      phantom; a glimmering; as, not a ghost of a chance; the
      ghost of an idea.

            Each separate dying ember wrought its ghost upon the
            floor.                                --Poe.

   4. A false image formed in a telescope by reflection from the
      surfaces of one or more lenses.

   {Ghost moth} (Zo["o]l.), a large European moth {(Hepialus
      humuli)}; so called from the white color of the male, and
      the peculiar hovering flight; -- called also {great
      swift}.

   {Holy Ghost}, the Holy Spirit; the Paraclete; the Comforter;
      (Theol.) the third person in the Trinity.

   {To} {give up or yield up} {the ghost}, to die; to expire.

            And he gave up the ghost full softly. --Chaucer.

            Jacob . . . yielded up the ghost, and was gathered
            unto his people.                      --Gen. xlix.
                                                  33.

Ghost \Ghost\, v. i.
   To die; to expire. [Obs.] --Sir P. Sidney.

Ghost \Ghost\, v. t.
   To appear to or haunt in the form of an apparition. [Obs.]
   --Shak.

Source : WordNet®

ghost
     v 1: move like a ghost; "The masked men ghosted across the
          moonlit yard"
     2: haunt like a ghost; pursue; "Fear of illness haunts her"
        [syn: {haunt}, {obsess}]
     3: write for someone else; "How many books have you
        ghostwritten so far?" [syn: {ghostwrite}]

ghost
     n 1: a mental representation of some haunting experience; "he
          looked like he had seen a ghost"; "it aroused specters
          from his past" [syn: {shade}, {spook}, {wraith}, {specter},
           {spectre}]
     2: a writer who gives the credit of authorship to someone else
        [syn: {ghostwriter}]
     3: the visible disembodied soul of a dead person
     4: a suggestion of some quality; "there was a touch of sarcasm
        in his tone"; "he detected a ghost of a smile on her face"
        [syn: {touch}, {trace}]

Source : Free On-Line Dictionary of Computing

ghost
     
         (Or "zombie") The image of a user's session on {IRC}
        and similar systems, left when the session has been terminated
        (properly or, often, improperly) but the server (or the
        network at large) believes the connection is still active and
        belongs to a real user.
     
        Compare {clonebot}.
     
        (1997-04-07)