顶石
Capstone \Cap"stone`\, n. (Paleon.) A fossil echinus of the genus {Cannulus}; -- so called from its supposed resemblance to a cap.
capstone n 1: a final touch; a crowning achievement; a culmination [syn: {finishing touch}, {copestone}] 2: a stone that forms the top of wall or building [syn: {copestone}, {coping stone}, {stretcher}]