Source : Webster's Revised Unabridged Dictionary (1913)

Pyrophosphoric \Pyr`o*phos*phor"ic\, a. [Pyro- + phosphoric.]
   (Chem.)
   Pertaining to, or designating, an acid, {H4P2O7}, which is
   obtained as a white crystalline substance. Its salts are
   obtained by heating the phosphates.