A musical tonic (7)
I believe the answer is:
keynote
This clue might be a double definition.
'a musical' is the first definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'tonic' is the second definition.
(I know that tonic can be written as keynote)
Can you help me to learn more?
(Other definitions for keynote that I've seen before include "Gist" , "The central speech of a conference" , "Central theme" , "Determining principle in a speech" , "of fundamental importance" .)