- 1 [intransitive] react (to something) (by doing something) to change or behave in a particular way as a result of or in response to something Local residents reacted angrily to the news. I nudged her but she didn't react. You never know how he is going to react. The market reacted by falling a further two points.
- 2 [intransitive] (+ adv./prep.) to become ill after eating, breathing, etc. a particular substance People can react badly to certain food additives.
- 3[intransitive] react (with something) react (together) (chemistry) (of substances) to experience a chemical change when coming into contact with another substance Iron reacts with water and air to produce rust. When an acid and an alkali react together the result is a salt and water. Phrasal Verbsreact against somebody/something
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NAmE//riˈækt//Verb Forms present simple I / you / we / they react
he / she / it reacts
past simple reacted
-ing form reacting