1. Also called orthoboric acid. Chem., Pharm.a white, crystalline acid, H3BO3, occurring in nature or prepared from borax: used chiefly in the manufacture of ceramics, cements, glass, and enamels, for fireproofing, and in medicine in aqueous solution as a mild antiseptic.
2. Chem.any of a group of acids containing boron.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.