Singer keen to make a comeback (4)
I believe the answer is:
diva
'singer' is the definition.
(diva can mean a female opera singer)
'keen to make a comeback' is the wordplay.
'keen' becomes 'avid' (both can mean enthusiastic).
'to make a comeback' says the letters should be written in reverse.
'avid' in reverse letter order is 'DIVA'.
(Other definitions for diva that I've seen before include "Avid like opera singer" , "A female opera singer" , "Prima dona" , "Grand female singer" , "Top opera singer" .)