"La Mer” composer (7)
I believe the answer is:
debussy
'la mer composer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for debussy that I've seen before include "Clair de Lune composer" , "Claude -, C. nineteen-twenty French composer" , "Claude, impressionist composer" , "Note-writer" , "Claude -, Fr. composer" .)