One isn't fit to be on it (4,4)
I believe the answer is:
sick list
This clue might be a double definition.
'one isn't fit' is the first definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's a link between them I don't understand?
'be on it' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for sick list that I've seen before include "Register of those ill" , "An enumeration of those who are ill" , "On which unwell are recorded" .)