1. (verb)react, respond show a response or a reaction to something Synonyms: respond, reply, react, oppose, answer
2. (verb)react, oppose act against or in opposition to Synonyms: respond, oppose, counterbalance, defend, pit, fight, fight back, react, play off, contradict, match, fight down, controvert
3. (verb)react undergo a chemical reaction; react with another substance under certain conditions Synonyms: respond, oppose