Performer full of enthusiasm in retirement (4)
I believe the answer is:
diva
'performer' is the definition.
(diva is a kind of performer)
'full of enthusiasm in retirement' is the wordplay.
'full of enthusiasm' becomes 'avid' (I've seen this in another clue).
'in retirement' says the letters should be written in reverse (retire can mean to go back or backwards).
'avid' reversed gives 'DIVA'.
(Other definitions for diva that I've seen before include "Avid like opera singer" , "Great performer" , "Famous female singer" , "One who sings" , "Operatic female singer" .)