Beethoven opera (7)
I believe the answer is:
fidelio
'beethoven opera' is the definition.
(Fidelio is an opera by Ludwig van Beethoven)
This is the entire clue.
(Other definitions for fidelio that I've seen before include "Noted work" , "18 OPERA]" , "Beethoven opera; I.e. if old (anag.)" , "Beethoven's only opera" , "Noted performance" .)