An explosive utterance (5)
I believe the answer is:
blast
'an explosive utterance' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I can't see?
This is the entire clue.
Can you help me to learn more?
(Other definitions for blast that I've seen before include "Mild expletive - sharp explosion" , "Sudden strong gust of wind" , "Effect of explosion" , "Great time: explosion" , "Blow up with explosives" .)