• (a.) Of, pertaining to, or designating, a thionic derivative, H/S/O/, of sulphuric acid, obtained as a colorless, odorless liquid.
Tet`ra·thi·on'ic adjective [ Tetra- + thionic .] (Chemistry) Of, pertaining to, or designating, a thionic derivative, H 2 S 4 O 6 , of sulphuric acid, obtained as a colorless, odorless liquid.