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"substance which speeds a chemical reaction but itself remains unchanged," 1902, formed in English (on analogy of analyst) from catalysis. Figurative use by 1943.
catalyst cat·a·lyst (kāt'l-ĭst)n. A substance, usually used in small amounts relative to the reactants, that modifies and increases the rate of a reaction without being consumed in the process.
In chemistry, a substance that causes a chemical reaction to occur but is not itself involved in the reaction.
Note: The term catalyst is often used to refer to the prime agent of any change: “She was the catalyst for the reorganization.”