A dud rhyme is far from clear (3)
I believe the answer is:
mud
'a dud rhyme' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
I don't understand the rest of the clue.
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" .)