catalyst - (chemistry) a substance that initiates or accelerates a chemical reaction without itself being affectedchemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions activator - (biology) any agency bringing about activation; a molecule that increases the activity of an enzyme or a protein that increases the production of a gene product in DNA transcription enzyme - any of several complex proteins that are produced by cells and act as catalysts in specific biochemical reactions platinum black - a fine black powder of platinum; used as a catalyst in chemical reactions anticatalyst - (chemistry) a substance that retards a chemical reaction or diminishes the activity of a catalyst |