1. the central wedge-shaped stones at the top of arches that lock the other stones in place
Usage: architecture
2. the most important parts of policies, systems, or beliefs on which everything else depends
Usage: figurative

Examples

• The ancient Roman bridge’s keystones have held the structure together for centuries.
• Workers carefully positioned the keystones to complete the stone archway.
• Education and healthcare are the keystones of their social policy.
• Trust and communication serve as the keystones of any successful relationship.
• The keystones of the cathedral’s arches were carved with intricate designs.
• Economic stability and job creation are keystones of the mayor’s platform.