Signalling system (9)
I believe the answer is:
semaphore
'signalling system' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for semaphore that I've seen before include "Way to signal" , "Strangely, home as per a system of communication" , "Signalling system using flags" , "Hears poem about arm signalling system" , "System of signalling with the arms" .)