What is pertaining to, or designating, a monobasic acid, HPO3, analogous to nitric acid, and, by heating phosphoric acid, obtained as a crystalline substance, commonly called glacial phosphoric acid called?

metaphosphoric — Pertaining to, or designating, a monobasic acid, HPO3, analogous to nitric acid, and, by heating phosphoric acid, obtained as a crystalline substance, commonly called glacial phosphoric acid. (Webster's 1913.)

Sources