Strong's G4557 · Greek

σαρδόνυξ

sardonux · sar-don'-oox

from the base of 4556 and onux (the nail of a finger; hence the "onyx" stone); a "sardonyx", i.e. the gem so called

Scholarly Lexicons

Abbott-Smith Manual Greek Lexicon

 1 * σαρδόνυξ (L, σαρδιόνυξ ), -υχος, ὁ ( σάρδιον , ὄνυξ ), sardonyx , a stone marked by the red of the sard and the white of the onyx: Re 21:20 .† 

G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain