noun
: any of numerous acids that are characterized by the sulfonic group and may be regarded as derived from sulfuric acid by replacement of a hydroxyl group by either an inorganic anion or a univalent organic radical ; especially : any of a class of organic acids (as toluenesulfonic acids or phenolsulfonic acids) that have the general formula RSO 3 H when only one sulfonic group is present, that are in general stable, easily water-soluble, strong acids, that are made especially in the case of the aromatic acids by direct sulfonation, and that are used often in the form of salts chiefly as catalysts, detergents, and intermediates (as for dyes) — compare chlorosulfonic acid , petroleum sulfonate , sulfinic acid