Source : Webster's Revised Unabridged Dictionary (1913)

Dithionic \Di`thi*on"ic\, a. [Pref. di- + -thionic.] (Chem.)
   Containing two equivalents of sulphur; as, dithionic acid.

   {Dithionic acid} (Chem.), an unstable substance, {H2S2O6},
      known only in its solutions, and in certain well-defined
      salts.