keystone, key block meaning

[Architecture]
1.

The central voussoir of an arch, which is often embellished; until the keystone is in place, no true arch action takes place.

2.

An element resembling a keystone in function or in shape.

keystone, 1: K

• key block:    [Architecture]A ke ...
• keystone:    Noun: keystone&nbs ...
• keystone arch:    [Architecture]Any ...