Like this list of letters? (6)
I believe the answer is:
italic
'like this list of letters?' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
This is the entire clue.
Can you help me to learn more?
(Other definitions for italic that I've seen before include "not exactly an upright type" , "typifies a list in character" , "more oblique than Roman" , "Letters written sloping to the right" , "Sloping (writing)" .)