Councils of bishops (6)
I believe the answer is:
synods
'councils of bishops' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for synods that I've seen before include "Council to discuss ecclesiastical business" , "Council meetings of clergy to discuss policy" , "Councils of bishops" , "Ecclesiastical councils" , "Councils attended by clergy to discuss policy" .)