Donor arranged for the musical composition (5)
I believe the answer is:
rondo
'the musical composition' is the definition.
(I've seen this before)
'donor arranged' is the wordplay.
'arranged' is an anagram indicator.
'donor' with letters rearranged gives 'RONDO'.
'for' acts as a link.
(Other definitions for rondo that I've seen before include "Repetitive musical form" , "Piece of music, often of the last movement" , "Music form with recurring theme" , "Piece of music with repeated refrain" , "Donor (anag) - piece of music" .)