Sulphur trioxide Meaning, Definition & Usage

Definitions
  1. (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.

Webster 1913