The sin apt to corrupt one who is naturally religious? (9)
I believe the answer is:
pantheist
'one who is naturally religious?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'the sin apt to corrupt' is the wordplay.
'to corrupt' indicates anagramming the letters (a corrupted form).
'the'+'sin'+'apt'='thesinapt'
'thesinapt' is an anagram of 'PANTHEIST'.
Can you help me to learn more?
(Other definitions for pantheist that I've seen before include "Believer in many gods" , "everything one believes in?" , "Spinoza was one" , "Believer that god is in everything - even in Athens pit" .)