(n.) 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's Revised Unabridged Dictionary
| APA | Webster's. (2011). keystone. Retrieved September 21, 2026, from http://smartdefine.org/keystone/definitions/2025343 |
| Chicago | Webster's. 2011. "keystone" http://smartdefine.org/keystone/definitions/2025343 (accessed September 21, 2026). |
| Harvard | Webster's 2011, keystone, Smart Define, viewed 21 September, 2026, <http://smartdefine.org/keystone/definitions/2025343>. |
| MLA | Webster's. "keystone" 27 May 2011. Web. 21 September 2026. <http://smartdefine.org/keystone/definitions/2025343> |