Silence, be still (4)
I believe the answer is:
hush
I believe this clue is a double definition.
'silence' is the first definition.
(I know that silence can be written as hush)
'be still' is the second definition.
(I've seen this in another clue)
(Other definitions for hush that I've seen before include "Mum's the word" , "Make (someone) quiet" , "Make or become silent or quiet" , "Quieten" , "Soothe" .)