Tornado sound (4)
I believe the answer is:
roar
'tornado sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for roar that I've seen before include "Lion's call" , "The __ of the Greasepaint -- The Smell of the Crowd (1964 musical)" , "Jaguar, for example, emits this" , "Make a loud noise" , "engine noise" .)