metantimonic

from The Century Dictionary.

• Noting an acid, HSbO₃, obtained by heating ortho-antimonic acid to 175° C. The metantimonic acid of Frémy (H₄Sb₂O₇) is now called pyro-antimonic acid, thus preserving analogy with the different phosphoric acids.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Pertaining to, or designating, an acid (formerly called antimonic acid) analogous to metaphosphoric acid, and obtained as a white amorphous insoluble substance, (HSbO3).
• adjective Formerly, designating an acid, which is now properly called pyroantimonic acid, and analogous to pyrophosphoric acid.