pyroboric

from The Century Dictionary.

• Noting an acid, H₂B₄O₇, obtained as a glass-like brittle mass by heating orthoboric or boracic acid for a long time to 140° C.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Of or relating to pyroboric acid or its derivatives.