Bishop's headgear (5)
I believe the answer is:
mitre
'bishop's headgear' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mitre that I've seen before include "Item of headgear" , "Corner joint - bishop's hat" , "episcopal head may come under this" , "symbol of ecclesiastical authority" , "A bishop wears it" .)