...is very keen to make a comeback (4)
I believe the answer is:
diva
'is very' is the definition.
I can't judge whether this defines the answer.
'keen to make a comeback' is the wordplay.
'keen' becomes 'avid' (I've seen this before).
'to make a comeback' says the letters should be written backwards (I've seen 'making a comeback' mean this).
'avid' back-to-front is 'DIVA'.
(Other definitions for diva that I've seen before include "High-maintenace woman" , "Prima dona" , "Female opera star" , "Operatic ego" , "Great performer" .)