Churchman's official list (5)
I believe the answer is:
canon
This could be a double definition.
'churchman's' is the first definition.
(I've seen this in another clue)
'official list' is the second definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for canon that I've seen before include "Rule -- principle" , "accepted criterion" , "Standard" , "General principle or kind of clergyman" , "Senior clergyman" .)