Heathen cool with arcane field (7)
I believe the answer is:
infidel
'heathen' is the definition.
(I know this)
'cool with arcane field' is the wordplay.
I cannot quite see how this works, but
'cool' could be 'in' ('in' can mean fashionable or cool) and 'in' is located in the answer.
an anagram of 'field' is 'fidel' which is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for infidel that I've seen before include "Literally, 9 [UNFAITHFUL]" , "Person rejecting a specific religion" , "Non-believer, heretic" , "One not believing" , "Person who does not believe in a religion" .)