/ riˈækt; NAmE / verb [ v ]
1.
react (to sth) (by doing sth) to change or behave in a particular way as a result of or in response to sth :
Local residents have 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.
to become ill / sick after eating, breathing, etc. a particular substance :
People can react badly to certain food additives.
3.
react (with sth) | 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.
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PHRASAL VERBS
- react against sb/sth
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WORD ORIGIN
mid 17th cent.: from re- (expressing intensive force or reversal) + act , originally suggested by medieval Latin react- done again, from the verb reagere .