Messiah composer (6)
I believe the answer is:
handel
'messiah composer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for handel that I've seen before include "Water Music composer, d. 1759" , "German composer, George Frederick (1685-1759)" , "British composer of German birth, the 'father of the oratorio'" , "Old musician" , "German scorer" .)