1 [C,U] (a) reaction (to sb/sth) something that you do or say because of sth that has happened 反应；回应: Could we have your reaction to the latest news, Prime Minister? 首相先生，能不能告诉我们你对这个最新消息有什么反应？I shook him to try and wake him up but there was no reaction. 我摇摇他想把他弄醒，但他没有反应。

2 [C,U] (a) reaction (against sb/sth) behaviour that shows that you do not like the influence of sb/sth (for example authority, your family, etc) （对当权者、家庭等的）反抗，反对

3 [C] a reaction (to sth) a bad effect that your body experiences because of sth that you have eaten, touched or breathed （吃、触摸、吸入某物后产生的）不良反应，不舒服: She had an allergic reaction to something in the food. 她对食物里的某种东西有过敏反应。

4 [C] [usu.pl] the physical ability to act quickly when sth happens 本能的反应: If the other driver's reactions hadn't been so good, there would have been an accident. 如果另外那个司机的反应不这么快，早就发生事故了。

5 [C,U] (technical术语) a chemical change produced by two or more substances coming into contact with each other （两种或以上物质接触后所产生的）化学反应，化学作用