Initial combination that's familiar in a mass (7)
I believe the answer is:
acronym
'initial combination' 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?
'familiar in a mass' is the wordplay.
'familiar' becomes 'crony' (I can't justify this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'a'+'m'='am'
'crony' going within 'am' is 'ACRONYM'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for acronym that I've seen before include "UNICEF, perhaps" , "Word made from initial letters of other words" , "Radar or Nato, maybe" , "Word made form first letters of other words" , "Ernie, perhaps" .)