Gesture of great importance (6)
I believe the answer is:
signal
I believe this clue is a double definition.
'gesture' is the first definition.
(I've seen this in another clue)
'of great importance' is the second definition.
(signal can mean important or significant)
(Other definitions for signal that I've seen before include "Non-verbal communication" , "Important; communication" , "Nonverbal action or gesture that encodes a message" , "Indicate" , "Aligns (anag) -- gesture" .)