Unaccompanied choral composition (5)
I believe the answer is:
motet
'unaccompanied choral composition' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for motet that I've seen before include "Certain one is morally superior" , "Piece of sacred music" , "Short sacred vocal work" , "Totem (anag) ? anthem" , "Unaccompanied choral composition with sacred lyrics" .)