A substance that diminishes the rate of a chemical reaction; the process is called inhibition. Inhibitors are sometimes called negative catalysts, but since the action of an inhibitor is fundamentally different from that of a catalyst, this terminology is discouraged. In contrast to a catalyst, an inhibitor may be consumed during the course of a reaction. In enzyme-catalysed reactions an inhibitor frequently acts by binding to the enzyme, in which case it may be called an enzyme inhibitor.
See also: effector
PAC, 1993, 65, 2291. 'Nomenclature of kinetic methods of analysis (IUPAC Recommendations 1993)' on page 2295 (https://doi.org/10.1351/pac199365102291)