The Collaborative International Dictionary of English v.0.48:

Hyposulphurous \Hy`po*sul"phur*ous\, a. [Pref. hypo- +
   sulphurous.] (Chem.)
   Pertaining to, or containing, sulphur, all, or a part, in a
   low state of oxidation.
   [1913 Webster]

   Hyposulphurous acid.
   (a) Thiosulphuric acid. [Obs.]
   (b) An acid, H2SO2, obtained by the reduction of sulphurous
       acid. It is not obtained in the free state, but in an
       orange-yellow water solution, which is a strong reducing
       and bleaching agent. Called also hydrosulphurous acid.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thiosulphuric \Thi`o*sul*phur"ic\, a. [Thio- + sulphuric.]
   (Chem.)
   Of, pertaining to, or designating, an unstable acid,
   H2S2O3, analogous to sulphuric acid, and formerly called
   hyposulphurous acid.
   [1913 Webster]