ring stone

American  

noun

1. a voussoir appearing on a face of an arch.

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Example Sentences

Gazing into a ball of crystal or glass, a crystal or other smooth ring stone, such as a sapphire or ruby, or even into a common ink-pot, they will see visions very brilliant. 

From The Book of Dreams and Ghosts by Lang, Andrew

The scarabaeoid in its turn is abandoned for the simple ring stone.

From Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 5 "Gassendi, Pierre" to "Geocentric" by Various

A true topaz crystal was too hard for the ring stone, whose edge slipped over the smooth topaz surface.

From A Text-Book of Precious Stones for Jewelers and the Gem-Loving Public by Wade, Frank Bertram

The matter being thus introduced, the lady was at once informed that even a real emerald might show signs of wear after a few years of the hard use that comes to a ring stone.

From A Text-Book of Precious Stones for Jewelers and the Gem-Loving Public by Wade, Frank Bertram