Assembly of cardinals (8)
I believe the answer is:
conclave
'assembly of cardinals' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for conclave that I've seen before include "An assembly of cardinals to elect pope" , "Papal election meeting" , "Private meeting, perhaps of cardinals" , "Group meeting (to choose a pope?)" , "Secret assembly" .)