The Collaborative International Dictionary
Thionic
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.
Wiktionary
thionic
a. Of or pertaining to sulfur