One French composer become undone (7)
I believe the answer is:
unravel
'become undone' is the definition.
(synonyms)
'one french composer' is the wordplay.
'one' becomes 'un' (northern English dialect form of 'one').
'french composer' becomes 'ravel' (I've seen this before).
'un'+'ravel'='UNRAVEL'
(Other definitions for unravel that I've seen before include "Solve the problem" , "Unpick, untangle" , "Disentangle or undo like knitted fabric" , "Straighten out" , "Make sense of" .)