I come up to a matter of trivial importance (4)
I believe the answer is:
iota
'matter of trivial importance' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'i come up to a' is the wordplay.
'come up' is a reversal indicator.
'to' in reverse letter order is 'ot'.
'i'+'ot'+'a'='IOTA'
Can you help me to learn more?
(Other definitions for iota that I've seen before include "Smidgeon" , "very small part" , "Ninth Greek character" , "Just a jot, from Greek alphabet" , "Ninthe letter of the Greek alphabet" .)