The stone that caps or tops a wall, fence, or structure; a coping stone that provides the finishing layer.
From 'cope' (the top/coping of a wall, from Old English) + 'stone.' 'Cope' itself derives from Old French and Old English terms for a covering or hood-like structure.
Copestones are architecturally crucial—they shed water away from the wall below, so a crumbling copestone can lead to the entire wall's deterioration, which is why preservationists prioritize them when restoring historic buildings.
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