I believe the answer is:
This clue is a double definition.
'music' is the first definition.
(I know that opus is a type of music)
'work' is the second definition.
(an opus is an artistic work)
(Other definitions for opus that I've seen before include "(Numbered) musical composition" , "Soup (anag.)" , "Artistic work" , "Work (of a composer?)" , "Piece of music (with number)" .)