Terrible mistake started with massage (7)
I believe the answer is:
rubbish
'terrible mistake' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'started with massage' is the wordplay.
'started' becomes 'bish' (I am not sure about this - if you are sure you should believe this answer much more).
'with' is a charade indicator (letters next to each other).
'massage' becomes 'rub' (rub can mean to massage).
'bish' after 'rub' is 'RUBBISH'.
Can you help me to learn more?
(Other definitions for rubbish that I've seen before include "Refuse, junk" , "Dross - twaddle" , "of exceedingly low quality" , "Litter or nonsense" , "Worthless material or nonsensical talk" .)