Source : Webster's Revised Unabridged Dictionary (1913)

Cerargyrite \Ce*rar"gy*rite\, n. [Gr. ? horn + ? silver.] (Min.)
   Native silver chloride, a mineral of a white to pale yellow
   or gray color, darkening on exposure to the light. It may be
   cut by a knife, like lead or horn (hence called horn silver).