Though endlessly negative, it's of positive significance (3)
I believe the answer is:
nod
This clue could be a double definition.
'though endlessly negative' is the first definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
'of positive significance' is the second definition.
The definition suggests a singular noun which matches the answer.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for nod that I've seen before include "Land of exile" , "Signal assent" , "Tacit agreement" , "Agree non-verbally" , "Silent assent" .)