Speaks idly of Nato, terse, never coming to a conclusion (7)
I believe the answer is:
natters
'speaks' is the definition.
The definition and answer can be both to do with communicating as well as being verbs in their -s form.
Maybe you can see a link between them that I don't see?
I cannot understand how the rest of the clue works.
(Other definitions for natters that I've seen before include "Chatters" , "Talks idly" .)