Resentful about God (4)
I believe the answer is:
eros
'god' is the definition.
(I know that Eros is a Greek deity)
'resentful about' is the wordplay.
'resentful' becomes 'sore' (sore can mean resentful or annoyed).
'about' says the letters should be written backwards.
'sore' reversed gives 'EROS'.
(Other definitions for eros that I've seen before include "God of love - example of 1 down" , "asteroid four hundred and thirty three" , "Goddess" , "Arrow shooter" , "Greek name of Cupid" .)