Oratorio part (4)
I believe the answer is:
aria
'oratorio part' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aria that I've seen before include "Song for solo voice from an oratorio, cantata etc" , "Operatic solo performance" , "Operatic vocal" , "Operatic song" , "Vocal solo in a cantata etc" .)