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.
[1913 Webster]