The keystone in the crown of an arch.
拱顶石位于拱顶的塞缝石
A wooden frame built especially to support the sides of an arch until the keystone is positioned.
支拱板条专门用来在拱顶石放置好以前支撑拱的两边木架子
Belief in a life after death is the keystone of her religious faith.
她的宗教信仰的基础是相信死後有来生。