(n.) The central or topmost stone of an arch. This in some styles is made different in size from the other voussoirs, or projects, or is decorated with carving.

apse arcade arcature arch arched roof archway basis bench mark camber cardinal point ceilinged roof chief thing climax concameration concha core cornerstone cove crisis critical point crux cupola dome essence essential essential matter first stone footstone foundation foundation stone fundamental geodesic dome gist gravamen great point headstone heart high point igloo important thing issue kernel landmark main point main thing material point meat milestone necessity nub ogive pith pivot principle quoin real issue salient point sine qua non skewback span substance substantive point the bottom line the point turning point vault vaulting voussoir