It's religiously read (5)
I believe the answer is:
bible
'read' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for bible that I've seen before include "See 12" , "Holy Scripture" , "The Good Book" , "The Christian or Jewish scriptures" , "Book regarded as the ultimate authority on its subject" .)