A body called together to deliberate. From the shout that summons - a council is not a group that exists, but a group that was CALLED.
Latin concilium (an assembly, meeting), from com- (together) + calare (to call, summon); a body that exists only because it was called together, not one that simply happens to be present.
Its Latin root is a summons, not a standing body — concilium names the calling together, not the group once assembled. What sits at this house's councils exists only because something called it, and stops existing the moment nothing calls it back.