Joint in which the bishop's hat is found (5)
I believe the answer is:
mitre
'joint in which the bishop's hat is found' is the definition.
'mitre' can be an answer for 'joint' (mitre joint is a kind of joint). I am not sure about the rest of the definition.
'joint in which the' is the wordplay.
'joint' becomes 'mire' (I am not sure about this - if you are sure you should believe this answer much more).
'in which' indicates putting letters inside.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'mire' going around 't' is 'MITRE'.
Can you help me to learn more?
(Other definitions for mitre that I've seen before include "Timer (anag.)" , "A bishop's tall hat" , "episcopal head may come under this" , "bishop's head?" , "Bishop's headgear - joint" .)