Straighten out a French composer (7)
I believe the answer is:
unravel
'straighten out' is the definition.
(unraveling is a kind of straightening out)
'a french composer' is the wordplay.
'a french' becomes 'un' ('a' in French).
'composer' becomes 'ravel' (Maurice Ravel).
'un'+'ravel'='UNRAVEL'
(Other definitions for unravel that I've seen before include "Come undone; solve" , "Sort out" , "Disentangle or undo like knitted fabric" , "Become undone" , "Straighten out" .)