Source : Webster's Revised Unabridged Dictionary (1913)

Isethionic \I*seth`i*on"ic\, a. [Is- + ethionic.] (Chem.)
   Pertaining to, derived from, or designating, an acid,
   {HO.C2H4.SO3H}, obtained as an oily or crystalline substance,
   by the action of sulphur trioxide on alcohol or ether. It is
   derivative of sulphuric acid.