Chemistry 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.
One that precipitates a process or event, especially without being involved in or changed by the consequences: "A free press ... has remained ... a vital catalyst to an informed and responsible electorate” ( Robert O'Neal).
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.