Summer weather coming in, button up dress (6)
I believe the answer is:
sheath
'dress' is the definition.
(both can mean to cover up)
'summer weather coming in button up' is the wordplay.
'summer weather' becomes 'heat' (it's hot in the summer).
'coming in' means one lot of letters goes inside another.
'button up' becomes 'sh' (both can be used to tell someone to be quiet).
'heat' put into 'sh' is 'SHEATH'.
(Other definitions for sheath that I've seen before include "Holder for a dagger" , "coat" , "Covering for blade" , "cocktail dress" , "Scabbard" .)