\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.