A substance, other than the catalyst or one of the substrates, that increases the rate of a catalysed reaction without itself being consumed; the process is called activation. An activator of an enzyme-catalysed reaction may be called enzyme activator, if it acts by binding to the enzyme.
See also: effector
PAC, 1993, 65, 2291. 'Nomenclature of kinetic methods of analysis (IUPAC Recommendations 1993)' on page 2292 (https://doi.org/10.1351/pac199365102291)