Upset tender love god (4)
I believe the answer is:
eros
'love god' is the definition.
(Greek god of love)
'upset tender' is the wordplay.
'upset' says the letters should be written backwards.
'tender' becomes 'sore' (synonyms).
'sore' in reverse letter order is 'EROS'.
(Other definitions for eros that I've seen before include "Winged god of love" , "Form of love" , "capital statue" , "Greek god of love - see statue in Piccadilly" , "Deity" .)