Devil-worshipper (8)
I believe the answer is:
satanist
'devil-worshipper' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for satanist that I've seen before include "Saint sat with devil worshipper" , "One who worships the devil" , "diabolical fellow" , "Devil devotee" , "Devil-worshipper" .)