Heathen; irreligious (5)
I believe the answer is:
pagan
This clue is a double definition.
'heathen' is the first definition.
(both can mean an irreligious person)
'irreligious' is the second definition.
(similar in meaning)
(Other definitions for pagan that I've seen before include "One outside the main religions" , "A heathen, not a Christian" , "Person without any conventional religion" , "advocate of pleasures" , "Heathen; non-believer" .)