I come back to a matter of trivial importance (4)
I believe the answer is:
iota
'matter of trivial importance' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'i come back to a' is the wordplay.
'come back' is a reversal indicator.
'to' reversed gives 'ot'.
'i'+'ot'+'a'='IOTA'
Can you help me to learn more?
(Other definitions for iota that I've seen before include "Foreign character" , "Extremely small amount" , "The Greek i (4)" , "(Not one) little bit" , "A little piece" .)