Feature of retrograde love song (4)
I believe the answer is:
nose
'feature' is the definition.
(a facial feature)
'of retrograde love song' is the wordplay.
'retrograde' says the letters should be written backwards.
'of' indicates the answer is hidden within the clue.
'eson' is hidden in the letters of 'love song'.
'eson' backwards is 'NOSE'.
(Other definitions for nose that I've seen before include "Organ of face" , "In-your-face" , "Asian wind instrument -- use Teflon (anag)" , "Facial organ" , "Front of plane" .)