Source : Webster's Revised Unabridged Dictionary (1913)

   2. (Geom.) A rhombohedron.

   {Fresnel's rhomb} (Opt.), a rhomb or oblique parallelopiped
      of crown or St. Gobain glass so cut that a ray of light
      entering one of its faces at right angles shall emerge at
      right angles at the opposite face, after undergoing within
      the rhomb, at other faces, two reflections. It is used to
      produce a ray circularly polarized from a plane-polarized
      ray, or the reverse. --Nichol.