Eager singer to return (4)
I believe the answer is:
avid
'eager' is the definition.
('avid' can be a synonym of 'eager')
'singer to return' is the wordplay.
'singer' becomes 'diva' (diva is a kind of singer).
'to return' says the letters should be written backwards.
'diva' reversed gives 'AVID'.
(Other definitions for avid that I've seen before include "Extremely enthusiastic" , "Fervent" , "'Eager, zealous (4)'" , "Fanatical" , "Keenly interested" .)