The character of a communication (6)
I believe the answer is:
letter
I believe this clue is a double definition.
'the character' is the first definition.
(letter is a kind of character)
'a communication' is the second definition.
(letter is a kind of communication)
'of' is the link.
(Other definitions for letter that I've seen before include "Character - mail - landlord" , "Alphabetic character" , "reference?" , "Eg, A" , "Character - landlord - epistle" .)