Terribly avid performer (4)
I believe the answer is:
diva
'performer' is the definition.
(diva is a kind of performer)
'terribly avid' is the wordplay.
'terribly' indicates an anagram.
'avid' anagrammed gives 'DIVA'.
(Other definitions for diva that I've seen before include "Great singer" , "A female opera singer" , "Female opera star" , "Famous female singer" , "High-maintenance opera singer?" .)