Composition for one (4)
I believe the answer is:
solo
'composition for one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for solo that I've seen before include "Alone - card game" , "Alone, unaccompanied" , "Type of whist" , "Unaccompanied passage" , "something for one to do" .)