Merriam-Webster Collegiate Dictionary - sulfur

 also sulphur  noun  Etymology: Middle English sulphur brimstone, from Latin sulpur, sulphur, ~  Date: 14th century a nonmetallic element that occurs either free or combined especially in sulfides and sulfates, is a constituent of proteins, exists in several allotropic forms including yellow orthorhombic crystals, resembles oxygen chemically but is less active and more acidic, and is used especially in the chemical and paper industries, in rubber vulcanization, and in medicine for treating skin diseases — see element table  • ~y or sulphury adjective Usage:  The spelling ~ predominates in United States technical usage, while both ~ and sulphur are common in general usage. British usage tends to favor sulphur for all applications. The same pattern is seen in most of the words derived from ~.