Joint headgear (5)
I believe the answer is:
mitre
I believe this is a double definition.
'joint' is the first definition.
(I know that mitre is a type of joint)
'headgear' is the second definition.
(I know that mitre is a type of headgear)
(Other definitions for mitre that I've seen before include "Corner joint - bishop's headdress" , "Timer (anag.)" , "Item of headgear" , "episcopal head may come under this" , "symbol of ecclesiastical authority" .)