Singular business! (7)
I believe the answer is:
agendum
This clue could be a double definition.
'singular' is the first definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'business' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
Can you help me to learn more?
(Another definition for agendum that I've seen is " item for meeting -".)