Deity doubter (8)
I believe the answer is:
agnostic
'deity doubter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for agnostic that I've seen before include "Religiously non-commital" , "He doesn't believe" , "One holding that knowledge of God is impossible" , "Coasting (anag)" , "Sceptic - unbelieving" .)