A brief show of dissent (4)
I believe the answer is:
demo
This clue might be a double definition.
'a brief show' is the first definition.
'demo' can be an answer for 'show' (I've seen this in another clue). I am not certain of the 'a brief' bit.
'dissent' is the second definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'of' acts as a link.
Can you help me to learn more?
(Other definitions for demo that I've seen before include "Protest (abbr)" , "Brass instrument valve" , "illustration" , "Protest march (sl.)" , "exhibit" .)