Eager, opera star to return (4)
I believe the answer is:
avid
'eager' is the definition.
(synonyms)
'opera star to return' is the wordplay.
'opera star' becomes 'diva' (diva can mean a female opera singer).
'to return' says the letters should be written in reverse.
'diva' reversed gives 'AVID'.
(Other definitions for avid that I've seen before include "Impassioned about diva" , "Extremely enthusiastic" , "Showing a very keen interest in something" , "Excessively keen" , "Mad for diva" .)