Greedy prima donna's upset (4)
I believe the answer is:
avid
'greedy' is the definition.
(synonyms)
'prima donna's upset' is the wordplay.
'prima donna' becomes 'diva' (synonyms).
'upset' says the letters should be written in reverse.
'diva' in reverse letter order is 'AVID'.
(Other definitions for avid that I've seen before include "Impassioned about diva" , "Fanatical" , "hungry" , "Keen, enthusiastic" , "Greatly desirous" .)