Composer's bottom rejected by topless minx (7)
I believe the answer is:
debussy
'composer's' is the definition.
(Claude Debussy)
'bottom rejected by topless minx' is the wordplay.
'bottom' becomes 'bed' ('bed' can be a synonym of 'bottom'**).
'rejected' says the letters should be written in reverse.
'by' is a charade indicator (letters next to each other).
'topless' means to remove the first letter.
'minx' becomes 'hussy'.
'bed' back-to-front is 'deb'.
'hussy' with its first letter removed is 'ussy'.
'deb'+'ussy'='DEBUSSY'
(Other definitions for debussy that I've seen before include "Clair de Lune composer" , "Note-writer" , "Claude, impressionist composer" , "Claude -, Fr. composer" , "Claude -, C. nineteen-twenty French composer" .)