Plainer? Darn rubbish! (10)
I believe the answer is:
balderdash
This clue could be a double definition.
'plainer? darn' is the first 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?
'rubbish' is the second definition.
(I've seen this in another clue)
Can you help me to learn more?
(Other definitions for balderdash that I've seen before include "Codswallop" , "Piffle" , "Rubbish" , "Claptrap" , "Poppycock" .)