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