Bishop's hat (5)
I believe the answer is:
mitre
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bishop's hat</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mitre that I've seen before include "Episcopal headdress" , "Bishop's headwear" , "Liturgical headdress" , "episcopal head may come under this" , "Bishop's cap - wood joint" .)