Court opening rarely unfilled (8)
I believe the answer is:
chancery
'court' is the definition.
(type of court)
'opening rarely unfilled' is the wordplay.
'opening' becomes 'chance' (I've seen this in other clues).
'unfilled' means to remove the middle letters.
'rarely' with its middle taken out is 'ry'.
'chance'+'ry'='CHANCERY'
(Other definitions for chancery that I've seen before include "Embassy/consulate office" , "Division of the High Court of Justice" , "Division of the British Court of Justice" , "Embassy office" , "Division of the British courts" .)