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.