A prima donna eager for retirement (4)
I believe the answer is:
diva
'a prima donna' is the definition.
(I know that prima donna can be written as diva)
'eager for retirement' is the wordplay.
'eager' becomes 'avid' (synonyms).
'for retirement' is a reversal indicator (retire can mean to retreat or go backwards).
'avid' back-to-front is 'DIVA'.
(Other definitions for diva that I've seen before include "Distinguished female singer" , "Great performer" , "One who sings" , "Avid like opera singer" , "Prima dona" .)