Keystone - Definition

n 1: a central cohesive source of support and stability; "faith
is his anchor"; "the keystone of campaign reform was the
ban on soft money"; "he is the linchpin of this firm" [syn:
anchor, mainstay, keystone, backbone, linchpin,
lynchpin]
2: the central building block at the top of an arch or vault
[syn: keystone, key, headstone]