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.

Source: Webster's Revised Unabridged Dictionary (1913)