The Collaborative International Dictionary of English v.0.48:

Metantimonic \Met`an*ti*mon"ic\, a. [Pref. met- + antimonic.]
   (Chem.)
   (a) Pertaining to, or designating, an acid (formerly called
       antimonic acid) analogous to metaphosphoric acid, and
       obtained as a white amorphous insoluble substance,
       (HSbO3).
   (b) Formerly, designating an acid, which is now properly
       called pyroantimonic acid, and analogous to
       pyrophosphoric acid.
       [1913 Webster]