Lion sound (4)
I believe the answer is:
roar
'lion sound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for roar that I've seen before include "Deep loud sound as of lion or bull" , "Loud noise of angry bull" , "Shout loudly" , "Lion's sound" , "Leonine bellow" .)