Flipping keen singer (4)
I believe the answer is:
diva
'singer' is the definition.
(diva is a kind of singer)
'flipping keen' is the wordplay.
'flipping' is a reversal indicator.
'keen' becomes 'avid' (I've seen this in other clues).
'avid' back-to-front is 'DIVA'.
(Other definitions for diva that I've seen before include "Successful lady" , "demanding woman" , "Operatic ego" , "Operatic female singer" , "Great singer" .)