pyrophosphoric acid

/P IH1 R AH0 F AA1 S F ER0 IH0 K AE0 S AH0 D/
noun
  1. 1

    A syrupy liquid formed by the dehydration of phosphoric acid; its salts, the pyrophosphates, are used in medicine.

  2. 2

    The acid formed by removing a molecule of water from two molecules of phosphoric acid, H4P2O7; this reaction slowly reverses in the presence of water.

Source: https://en.wiktionary.org/wiki/pyrophosphoric%20acid