\Sul"phur*ous\, a. [L. sulphurosus, sulfurosus: cf.
F. sulfureux.]
1. Of or pertaining to sulphur.
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.
{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}.