Warm up poultry for infidel (7)
I believe the answer is:
heathen
'for infidel' is the definition.
(synonyms)
'warm up poultry' is the wordplay.
'warm up' becomes 'heat' (I've seen this before).
'poultry' becomes 'hen' (hen is a kind of poultry).
'heat'+'hen'='HEATHEN'
(Other definitions for heathen that I've seen before include "Person lacking culture or moral principles" , "Savage" , "One who doesn't acknowledge your god" , "Barbaric" , "Godless person" .)