1. the uppermost stone in a structure, especially a wall or arch
Usage: architecture
2. the crowning achievement or final element that completes something
Usage: figurative

Examples

• The mason carefully placed the topstone on the garden wall.
• Each topstone was carved with intricate decorative patterns.
• The bridge’s topstone bore the date of its completion.
• Her doctoral thesis was the topstone of years of research.
• The peace treaty served as the topstone of the diplomatic negotiations.
• Without the topstone, the archway remained incomplete.