Cupid's tender return (4)
I believe the answer is:
eros
'cupid's' is the definition.
(I've seen this before)
'tender return' is the wordplay.
'tender' becomes 'sore' (synonyms).
'return' shows that the letters should be reversed in order.
'sore' written backwards gives 'EROS'.
(Other definitions for eros that I've seen before include "Greek equivalent to Roman Cupid" , "London landmark" , "God of love - example of 1 down" , "Cupid, to the Greeks" , "divinity" .)