Source : Webster's Revised Unabridged Dictionary (1913)

Pyroboric \Pyr`o*bo"ric\, a. [Pyro- + boric.] (Chem.)
   Pertaining to derived from, or designating, an acid, {H2B4O7}
   (called also {tetraboric} acid), which is the acid ingredient
   of ordinary borax, and is obtained by heating boric acid.