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Webster 1913 Edition

Keystone

Key′stoneˊ

,
Noun.
(Arch.)
The central or topmost stone of an arch. This in some styles is made different in size from the other voussoirs, or projects, or is decorated with carving. See Illust. of
Arch
.

Webster 1828 Edition

Keystone

KE'YSTONE

,
Noun.
The stone on the top or middle of an arch or vault, which being wider at the top than at the bottom, enters like a wedge and binds the work; properly, the fastening-stone.

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