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.