Source : Webster's Revised Unabridged Dictionary (1913)

Onycha \On"y*cha\, n. [NL., from L. onyx, -ychis, onyx, also, a
   kind of mussel, Gr. ?, ?. See {Onyx}.]
   1. An ingredient of the Mosaic incense, probably the
      operculum of some kind of strombus. --Ex. xxx. 34.

   2. The precious stone called onyx. [R.]