a. (Chem.) Pertaining to, or designating, an acid obtained by the reduction of sulphurous acid. See Hyposulphurous acid, under Hyposulphurous. [ 1913 Webster ]

a. [ Pref. hypo- + sulphurous. ] (Chem.) Pertaining to, or containing, sulphur, all, or a part, in a low state of oxidation. [ 1913 Webster ]

Hyposulphurous acid. (a) Thiosulphuric acid. [ Obs. ] (b) 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. [ 1913 Webster ]

a. [ L. sulphurosus, sulfurosus: cf. F. sulfureux. ] 1. Of or pertaining to sulphur. [ 1913 Webster ]

2. (Chem.) (a) Derived from, or containing, sulphur; specifically, designating those compounds in which the element has a lower valence as contrasted with the sulphuric compounds. (b) Having the characteristic odor of sulphur dioxide, or of hydrogen sulphide, or of other sulphur compounds. [ 1913 Webster ]

Sulphurous acid. (a) Sulphur dioxide. See under Sulphur. [ Obs. ] (b) An acid, H2SO3, not known in the free state except as a solution of sulphur dioxide in water, but forming a well-known series of salts (the sulphites). --
Sulphurous anhydride (Chem.), sulphur dioxide. See under Sulphur. [ 1913 Webster ]