- A substance that speeds up a chemical reaction without being consumed itself in the reaction.
- A substance that alters (usually increases) the rate at which a reaction occurs.
- a substance that accelerates a chemical reaction but does not become a part of the product produced
Source: Noland, George B. 1983. General Biology, 11th Edition. St. Louis, MO. C. V. Mosby
- A substance that promotes a chemical reaction by lowering the activation energy of a chemical reaction, but which itself remains unaltered at the end of the reaction.