Attack in numbers, about three (7)
I believe the answer is:
vitriol
'attack' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'numbers about three' is the wordplay.
'numbers' becomes 'viol' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'three' becomes 'tri' (prefix meaning 'three').
'viol' going around 'tri' is 'VITRIOL'.
'in' is the link.
Can you help me to learn more?
(Other definitions for vitriol that I've seen before include "Strong criticism" , "Bitter words" , "Sulphuric acid and hate-filled criticism" , "Sulphuric acid or savage criticism" , "Sulphuric acid and hateful criticism" .)