Bring back enthusiastic opera singer (4)
I believe the answer is:
diva
'opera singer' is the definition.
(thesaurus)
'bring back enthusiastic' is the wordplay.
'bring back' says the letters should be written in reverse.
'enthusiastic' becomes 'avid' ('avid' can be similar in meaning to 'enthusiastic').
'avid' back-to-front is 'DIVA'.
(Other definitions for diva that I've seen before include "fat lady?" , "Prima donna, woman opera singer" , "Operatic female singer" , "demanding woman" , "Great performer" .)