It shows the landlord's literal! (6)
I believe the answer is:
letter
'landlord's literal' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'it shows the' is the wordplay.
I cannot really understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
The remaining letters 'leer' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for letter that I've seen before include "Character - mail - landlord" , "Alphabetic symbol" , "reference?" , "he leases" , "Epistle, missive" .)