The Collaborative International Dictionary of English v.0.48:

Zirconia \Zir*co"ni*a\, n. [NL.] (Chem.)
   The oxide of zirconium (ZrO2), obtained as a white powder,
   and possessing both acid and basic properties. On account of
   its infusibility, and brilliant luminosity when incandescent,
   it is used as an ingredient of sticks for the Drummomd light.
   [1913 Webster]

   cubic zirconia. A colorless form of zirconia similar in
      appearance and refractivity to diamond, and used as a
      substitute for diamonds in inexpensive jewelry; -- also
      known by the acronym CZ.
      [PJC]

WordNet (r) 3.0 (2006):

zirconia
    n 1: a white crystalline oxide; used in refractories and in
         insulation and abrasives and enamels and glazes [syn:
         zirconium oxide, zirconia, zirconium dioxide]