keystone.

1. The central wedge-shaped stone at the top of an arch that helps hold its parts together.

2. An element on which a larger system, argument, or arrangement importantly depends.

Use it for

Words that belong together

• arch keystone
• carved keystone
• keystone at the crown

On the page

The keystone bore the date of the house’s construction.

A carved face looked down from the arch’s keystone.

The mason set the keystone at the crown of the arch.

Usage notes

Primary category: architecture. Forms: Singular keystone; plural keystones. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.