Religion renouncer (8)
I believe the answer is:
apostate
'religion renouncer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for apostate that I've seen before include "Julian was such" , "One no longer believing" , "One renouncing a belief" , "Person who deserts their religion" , "Turncoat" .)