ethionic

ethionic, a. Chem.
  (iːθɪˈɒnɪk)
  [f. ether) + Gr. θεῖον sulphur + -ic.
  Formed by Magnus in 1833, in imitation of the terms proto-, deuto-, trito-œnothionic [Gr. οἶνος wine], introduced by Sertuernor (1818) to designate three acids, one of which Magnus supposed to have been identical with ethionic acid.]
  ethionic acid: C₂H₆S₂O₇ (Watts Dict. Chem.) produced by the action of water on ethionic anhydride, C₂H₄2SO₃, formerly called sulphate of carbyl (Watts Dict. Chem.), which is obtained by bringing together olefiant gas and vapour of sulphuric anhydride in a tube.

Oxford English Dictionary