<p><strong>Noun</strong></p><ul><li>Chemistry: a substance that causes or accelerates a chemical reaction without itself being affected.</li><li>something that causes activity between two or more persons or forces without itself being affected.</li><li>a person or thing that precipitates an event or change: His imprisonment by the government served as the catalyst that helped transform social unrest into revolution.</li><li>a person whose talk, enthusiasm, or energy causes others to be more friendly, enthusiastic, or energetic.</li></ul>