Crossword Genius

Cupid's painful back (4)

Ross

I believe the answer is:

eros

'cupid's' is the definition.
(thesaurus)

'painful back' is the wordplay.
'painful' becomes 'sore' ('sore' can be a synonym of 'painful').
'back' says the letters should be written in reverse.
'sore' reversed gives 'EROS'.

(Other definitions for eros that I've seen before include "Form of love" , "Cupid's Greek alternative" , "Arrow-shooting god" , "Piccadilly 14 ac statue" , "One worshipped" .)

I've seen this clue in The Telegraph.
Want a hint initially instead of a full solution? Install my app