Emily Dickinson Lexicon

SAR'DON-YX, n. [L. sardonyches, from Gr. σαρδονυξ, from Sardis, a city of Asia Minor, and ονυξ, a nail; so named, according to Pliny, from the resemblance of its color to the flesh under the nail. Plin. Lib. 37, 6.]

A silicious stone or gem, nearly allied to carnelian. Its color is a reddish yellow, or nearly orange. We are informed that the yellow or orange colored agate, with an undulating surface, is now often called sardonyx. – Encyc. Cleaveland.