The Collaborative International Dictionary of English v.0.48:

Ghoul \Ghoul\ (g[=oo]l), n. [Per. gh[=o]l an imaginary sylvan
   demon, supposed to devour men and animals: cf. Ar. gh[=u]l,
   F. goule.]
   An imaginary evil being among Eastern nations, which was
   supposed to feed upon human bodies. [Written also ghole .]
   --Moore.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ghoul
    n 1: someone who takes bodies from graves and sells them for
         anatomical dissection [syn: graverobber, ghoul, body
         snatcher]
    2: an evil spirit or ghost

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "ghoul":
   Baba Yaga, Dracula, Frankenstein, Lilith, Wolf-man, afreet,
   ape-man, barghest, body snatcher, bogey, bogeyman, booster,
   bugaboo, bugbear, cacodemon, chicken thief, con man, crook, daeva,
   demon, den of thieves, devil, devil incarnate, dybbuk, embezzler,
   evil genius, evil spirit, fee-faw-fum, fiend, fiend from hell,
   filcher, frightener, ganef, genie, genius, ghost, grafter,
   grave robber, gyre, harpy, hellhound, hellion, hellkite, hobgoblin,
   holy terror, horror, incubus, jewel thief, jinni, jinniyeh, lamia,
   land pirate, land shark, land-grabber, larcener, larcenist, lifter,
   monster, nightmare, ogre, ogress, peculator, petty thief, phantom,
   pilferer, poacher, prowler, purloiner, rakshasa, revenant, robber,
   satan, scarebabe, scarecrow, scarer, scrounger, shedu, shoplifter,
   sneak thief, specter, stealer, succubus, swindler, terror,
   the undead, thief, vampire, werewolf, white-collar thief, yogini



The Devil's Dictionary (1881-1906):

GHOUL, n.  A demon addicted to the reprehensible habit of devouring
the dead.  The existence of ghouls has been disputed by that class of
controversialists who are more concerned to deprive the world of
comforting beliefs than to give it anything good in their place.  In
1640 Father Secchi saw one in a cemetery near Florence and frightened
it away with the sign of the cross.  He describes it as gifted with
many heads an an uncommon allowance of limbs, and he saw it in more
than one place at a time.  The good man was coming away from dinner at
the time and explains that if he had not been "heavy with eating" he
would have seized the demon at all hazards.  Atholston relates that a
ghoul was caught by some sturdy peasants in a churchyard at Sudbury
and ducked in a horsepond.  (He appears to think that so distinguished
a criminal should have been ducked in a tank of rosewater.)  The water
turned at once to blood "and so contynues unto ys daye."  The pond has
since been bled with a ditch.  As late as the beginning of the
fourteenth century a ghoul was cornered in the crypt of the cathedral
at Amiens and the whole population surrounded the place.  Twenty armed
men with a priest at their head, bearing a crucifix, entered and
captured the ghoul, which, thinking to escape by the stratagem, had
transformed itself to the semblance of a well known citizen, but was
nevertheless hanged, drawn and quartered in the midst of hideous
popular orgies.  The citizen whose shape the demon had assumed was so
affected by the sinister occurrence that he never again showed himself
in Amiens and his fate remains a mystery.