It's a far-reaching message, on paper (7)
I believe the answer is:
airmail
'paper' is the 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?
'it's a far-reaching message' is the wordplay.
'it's a far reaching' becomes 'air' (I can't justify this - if you can you should give a lot more credence to this answer).
'message' becomes 'mail' (mail is a kind of message).
'air'+'mail'='AIRMAIL'
'on' is the link.
Can you help me to learn more?
(Other definitions for airmail that I've seen before include "communication" , "Way of communicating" , "Letters carried by plane" , "I'm a liar (anag)" , "Flying post?" .)