Passage added on to a piece of music (4)
I believe the answer is:
coda
'passage added on to a piece of music' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for coda that I've seen before include "tail" , "Closing section of a musical composition" , "finale in Beethoven?" , "Ending of musical piece" , "Novel ending" .)