Source : Webster's Revised Unabridged Dictionary (1913)

Ethionic \Eth`i*on"ic\, a. [Ethyl + thionic.] (Chem.)
   Pertaining to, derived from, or designating, an acid so
   called.

   {Ethionic acid} (Chem.), a liquid derivative of
      ethylsulphuric and sulphuric (thionic) acids, obtained by
      the action of sulphur trioxide on absolute alcohol.