Large part of work - nearly the entirety - requiring singers (6)
I believe the answer is:
choral
'large part' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for choral that I've seen before include "Pertaining to a group of singers" , "For a large number of voices" , "Of a singing group" , "To do with group of singers, often in church" , "Involving many singers" .)