A dud rhyme is far from clear (3)
I believe the answer is:
mud
'a dud rhyme' is the definition.
The answer and definition 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?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for mud that I've seen before include "in your eye, it's an affable toast" , "Offensive remarks" , "Alluvial deposit as in river bed" , "soft soil" , "Muck - actionable remarks" .)