Order music (9,5)
I believe the answer is:
gregorian chant
This could be a double definition.
'order' is the first definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'music' is the second definition.
(Gregorian chant is an example)
Can you help me to learn more?
(Other definitions for gregorian chant that I've seen before include "variety of plainsong" , "Medieval plainsong" .)