Something a square peg can’t do (4)
I believe the answer is:
Here is my best explanation:
'do' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I don't see?
I cannot understand how the rest of the clue works.
(Other definitions for roll that I've seen before include "Rob while sleeping < to pass", "Bap", "bakery's product", "Bun", "Move on wheels - individual portion of bread", "See 19", "It may be called", "Official list; cylinder", "something on the drums" and "Cylinder (of paper etc)".)