What is "pyroantimonic acid"

Metantimonic \Met`an*ti*mon"ic\, a. [Pref. met- + antimonic.] (Chem.)

1. Pertaining to, or designating, an acid (formerly called antimonic acid) analogous to metaphosphoric acid, and obtained as a white amorphous insoluble substance, ( HSbO3).

2. Formerly, designating an acid, which is now properly called pyroantimonic acid, and analogous to pyrophosphoric acid.

n. (context chemistry English) An acid, H₄Sb₂O₇ derived from antimonic acid analogously to pyrophosphoric acid.