Gruesome fiend (5)
I believe the answer is:
ghoul
'gruesome fiend' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ghoul that I've seen before include "Corpse-loving phantom" , "Spirit that robs graves and devours corpses" , "malevolent spirit" , "Evil presence" , "Morbid voyeur" .)