Shell suit (4)
I believe the answer is:
case
I believe this is a double definition.
'shell' is the first definition.
('case' can be a synonym of 'shell')
'suit' is the second definition.
('case' can be a synonym of 'suit')
(Other definitions for case that I've seen before include "Judge tries this" , "Instance - container" , "Item of luggage" , "Legal action; container" , "Keep careful watch on" .)