Source : Webster's Revised Unabridged Dictionary (1913)

Thionic \Thi*on"ic\, a. [Gr. ? brimstone, sulphur.] (Chem.)
   Of or pertaining to sulphur; containing or resembling
   sulphur; specifically, designating certain of the thio
   compounds; as, the thionic acids. Cf. {Dithionic},
   {Trithionic}, {Tetrathionic}, etc.