Shortly put down one chapter in colloquial speech (7)
I believe the answer is:
demotic
'colloquial speech' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'shortly put down one chapter in' is the wordplay.
'shortly' means to remove the last letter.
'put down' becomes 'demote' (I've seen this before).
'one chapter in' becomes 'ic' (I can't explain this - if you can you should believe this answer much more).
'demote' with its final letter removed is 'demot'.
'demot'+'ic'='DEMOTIC'
Can you help me to learn more?
(Other definitions for demotic that I've seen before include "Colloquial; of the people" , "Of everyday language" , "Of language or writing, of the popular form" , "It'd come (anag) - of the common people" , "Colloquial language" .)