Keystone

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keystone

[′kē‚stōn]
(architecture)
Wedge-shaped stone at the crown of an arch.
(materials)
Small crushed stone used as filler for the large aggregate in bituminous bound roads.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Keystone

The central stone or voissoir at the top of the arch, the last part to be put into position to lock the arch in place, often embellished.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Keystone

 

in architecture, the stone or brick, usually wedge-shaped, at the top of an arch or vault. Its function is usually accentuated by ornamental patterns and carvings. A decorative keystone often adorns the flat lintel over the apertures of doors or windows. [9–963–l]

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

keystone, key block

keystone, 1: K
1. The central voussoir of an arch, which is often embellished; until the keystone is in place, no true arch action takes
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
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