It's not a positive answer (7)
I believe the answer is:
refusal
'a positive answer' is the 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?
'it's not' is the wordplay.
I cannot quite understand how this works, but
'it' could be 'sa' (SA can mean sex appeal, as in 'it') and 'sa' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for refusal that I've seen before include "problem for a show-jumper" , "Negative response" , "opportunity to accept or decline" , "Possibly first option to buy" , "Rejection; turning-down" .)