Tall headdress in corner joint (5)
I believe the answer is:
mitre
This clue might be a double definition.
'tall headdress' is the first definition.
'mitre' can be an answer for 'headdress' (mitre is a kind of headdress). I'm not sure about the 'tall' bit.
'corner joint' is the second definition.
(I've seen this before)
'in' is the link.
Can you help me to learn more?
(Other definitions for mitre that I've seen before include "Bishop's tall headdress" , "One identifies bishop" , "Bevelled joint that forms a corner" , "Episcopal headdress" , "What a bishop may have on" .)