Diplomatic tool for long distance communication (9)
I believe the answer is:
megaphone
'tool for long distance communication' is the definition.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for megaphone that I've seen before include "Voice-amplifying device" , "Funnel-shaped voice amplifier" , "Cone-shaped device to intensify the human voice" , "One projects sound" , "form of diplomacy?" .)