The Collaborative International Dictionary
hydrosulphurous acid
Hyposulphurous \Hy`po*sul"phur*ous\, a. [Pref. hypo- + sulphurous.] (Chem.) Pertaining to, or containing, sulphur, all, or a part, in a low state of oxidation. Hyposulphurous acid.
Thiosulphuric acid. [Obs.]
An acid, H2SO2, obtained by the reduction of sulphurous acid. It is not obtained in the free state, but in an orange-yellow water solution, which is a strong reducing and bleaching agent. Called also hydrosulphurous acid.
Wiktionary
hydrosulphurous acid
n. (alternative spelling of hydrosulfurous acid English)