Not any composition left unfinished! (4)
I believe the answer is:
none
'not any' is the definition.
(thesaurus)
'composition left unfinished' is the wordplay.
'composition' becomes 'nonet' (I've seen this before).
'left unfinished' means to remove the last letter.
'nonet' with its last letter removed is 'NONE'.
(Other definitions for none that I've seen before include "hour of prayer" , "Nobody - nothing" , "What's left after taking all" , "Not a soul" , "Zero" .)