The Collaborative International Dictionary of English v.0.48:

Sulphur \Sul"phur\, n. [L., better sulfur: cf. F. soufre.]
   1. (Chem.) A nonmetallic element occurring naturally in large
      quantities, either combined as in the sulphides (as
      pyrites) and sulphates (as gypsum), or native in volcanic
      regions, in vast beds mixed with gypsum and various earthy
      materials, from which it is melted out. Symbol S. Atomic
      weight 32. The specific gravity of ordinary octohedral
      sulphur is 2.05; of prismatic sulphur, 1.96.
      [1913 Webster]

   Note: It is purified by distillation, and is obtained as a
         lemon-yellow powder (by sublimation), called flour, or
         flowers, of sulphur, or in cast sticks called roll
         sulphur, or brimstone. It burns with a blue flame and a
         peculiar suffocating odor. It is an ingredient of
         gunpowder, is used on friction matches, and in medicine
         (as a laxative and insecticide), but its chief use is
         in the manufacture of sulphuric acid. Sulphur can be
         obtained in two crystalline modifications, in
         orthorhombic octahedra, or in monoclinic prisms, the
         former of which is the more stable at ordinary
         temperatures. Sulphur is the type, in its chemical
         relations, of a group of elements, including selenium
         and tellurium, called collectively the sulphur group,
         or family. In many respects sulphur resembles oxygen.
         [1913 Webster]

   2. (Zool.) Any one of numerous species of yellow or orange
      butterflies of the subfamily Pierinae; as, the clouded
      sulphur (Eurymus philodice syn. Colias philodice),
      which is the common yellow butterfly of the Eastern United
      States.
      [1913 Webster]

   Amorphous sulphur (Chem.), an elastic variety of sulphur of
      a resinous appearance, obtained by pouring melted sulphur
      into water. On standing, it passes back into a brittle
      crystalline modification.

   Liver of sulphur. (Old Chem.) See Hepar.

   Sulphur acid. (Chem.) See Sulphacid.

   Sulphur alcohol. (Chem.) See Mercaptan.

   Sulphur auratum [L.] (Old Chem.), a golden yellow powder,
      consisting of antimonic sulphide, Sb2S5, -- formerly a
      famous nostrum.

   Sulphur base (Chem.), an alkaline sulphide capable of
      acting as a base in the formation of sulphur salts
      according to the old dual theory of salts. [Archaic]

   Sulphur dioxide (Chem.), a colorless gas, SO2, of a
      pungent, suffocating odor, produced by the burning of
      sulphur. It is employed chiefly in the production of
      sulphuric acid, and as a reagent in bleaching; -- called
      also sulphurous anhydride, and formerly sulphurous
      acid.

   Sulphur ether (Chem.), a sulphide of hydrocarbon radicals,
      formed like the ordinary ethers, which are oxides, but
      with sulphur in the place of oxygen.

   Sulphur salt (Chem.), a salt of a sulphacid; a sulphosalt.


   Sulphur showers, showers of yellow pollen, resembling
      sulphur in appearance, often carried from pine forests by
      the wind to a great distance.

   Sulphur trioxide (Chem.), a white crystalline solid, SO3,
      obtained by oxidation of sulphur dioxide. It dissolves in
      water with a hissing noise and the production of heat,
      forming sulphuric acid, and is employed as a dehydrating
      agent. Called also sulphuric anhydride, and formerly
      sulphuric acid.

   Sulphur whale. (Zool.) See Sulphur-bottom.

   Vegetable sulphur (Bot.), lycopodium powder. See under
      Lycopodium.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sulphur dioxide
    n 1: a colorless toxic gas (SO2) that occurs in the gases from
         volcanoes; used in many manufacturing processes and present
         in industrial emissions; causes acid rain [syn: sulfur
         dioxide, sulphur dioxide]