Composer left after dance party (5)
I believe the answer is:
ravel
'composer' is the definition.
(Maurice Ravel)
'left after dance party' is the wordplay.
'left' becomes 'l' (common abbreviation).
'after' is a charade indicator (letters next to each other).
'dance party' becomes 'rave' (rave is a type of dance event).
'l' put after 'rave' is 'RAVEL'.
(Other definitions for ravel that I've seen before include "Make more complicated - French composer, d. 1937" , "Tangle or become tangled" , "note-writer observed" , "Tangle - untangle - French composer, d. 1937" , "Entangle - French composer, d. 1937" .)