Head supporting action by which to obtain a new name (4,4)
I believe the answer is:
deed poll
'head supporting action by which to obtain a new name' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'head supporting action' is the wordplay.
'head' becomes 'poll' (poll is a now rare word for head or scalp).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'action' becomes 'deed' (deed is a kind of action).
'poll' after 'deed' is 'DEED POLL'.
Can you help me to learn more?
(Other definitions for deed poll that I've seen before include "Legal document made and executed by one party only" , "By which legal names are changed?" , "means to change name" , "Legal action by one person, to change their name perhaps" , "I confirm new designation" .)