noun
keystone
KEY-stohn/ˈkiːstəʊn/
The central stone securing an arch's structure.
The wedge-shaped keystone locks the stones of the arch together.
Etymology
The key stone locks the other stones of an arch together. That structural role became an image for the chief element holding a system together.
In context
the arch is connected at its apex from both sides. In stone arches, the topmost stone is key to keeping the whole thing standing, and, of course, it’s called the keystone.
More examples
- The mason sets the keystone at the top of the arch.
- Each of the three arches has a carved keystone.
- A crack runs through the arch's keystone.
Forms
keystone · keystones
Similar words
- key
- An older architectural term for the same central arch stone.