Second experiment, soprano unused in choral music (5)
I believe the answer is:
motet
'music' is the definition.
(I have seen 'sacred music' mean 'motet' so perhaps 'music' could also mean 'motet')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for motet that I've seen before include "Polyphonic choral liturgical piece" , "Short sacred choral work" , "Church composition - totem (anag)" , "Musical composition" , "Church choral composition" .)