名詞 keystone:

1. a central cohesive source of support and stability
   同義詞：anchor, mainstay, backbone, linchpin, lynchpin
2. the central building block at the top of an arch or vault
   同義詞：key, headstone

1. The keystone in the crown of an arch.
   拱頂石位于拱頂?shù)娜p石
2. A wooden frame built especially to support the sides of an arch until the keystone is positioned.
   支拱板條專門用來在拱頂石放置好以前支撐拱的兩邊木架子
3. Belief in a life after death is the keystone of her religious faith.
   她的宗教信仰的基礎是相信死後有來生。

key.stone

n.（名詞）
Architecture The central wedge-shaped stone of an arch that locks its parts together.Also called headstone
【建筑學】 拱頂石，塞縫石：拱的中部楔形石頭，使拱的各個部分連在一起也作 headstone
The central supporting element of a whole.
基礎、主旨：整體的一個中心基本原則