Source : Webster's Revised Unabridged Dictionary (1913)

Tetrathionic \Tet`ra*thi*on"ic\, a. [Tetra- + thionic.] (Chem.)
   Of, pertaining to, or designating, a thionic derivative,
   H?S?O?, of sulphuric acid, obtained as a colorless, odorless
   liquid.