It's a handicap in a manner of speaking (7)
I believe the answer is:
stammer
'speaking' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stammer that I've seen before include "Psychological speech problem" , "Speak with difficulty" , "delivery problem" , "Involuntary speech mannerism" , "Disorder" .)