“+...- noun
Etymology: pyrophosphoric International Scientific Vocabulary pyr- + phosphoric
: a crystalline acid H 4 P 2 O 7 that is formed when orthophosphoric acid is heated and is prepared in the form of salts by heating acid salts of orthophosphoric acid and that dissociates above its melting point into orthophosphoric acid and polyphosphoric acids — called also diphosphoric acid