1. a stone that forms the top of a wall or building; a coping stone
Usage: architecture
2. the finishing touch or crowning achievement of something
Usage: figurative

Examples

• The mason carefully placed each copestone along the garden wall.
• Weather had worn away the mortar holding the copestones in place.
• The ancient castle’s copestones were carved with intricate designs.
• His Nobel Prize was the copestone of a brilliant scientific career.
• The final chapter served as the copestone to her trilogy.
• The peace treaty was the copestone of years of diplomatic effort.