Simple Definition of react
: to behave or change in a particular way when something happens, is said, etc.
of a chemical substance : to change after coming into contact with another substance
medical : to be affected by a drug, food, etc., in usually a bad way
Full Definition of react
1 : to exert a reciprocal or counteracting force or influence —often used with on or upon
2 : to change in response to a stimulus
3 : to act in opposition to a force or influence —usually used with against
4 : to move or tend in a reverse direction
5 : to undergo chemical reaction
: to cause to react
Examples of react in a sentence
When I told her what happened, she reacted with anger.
I didn't expect him to react that way.
The firefighters reacted quickly when they heard the alarm.
He reacted badly to the drug.
Origin and Etymology of react
New Latin reactus, past participle of reagere, from Latin re- + agere to act — more at agent
First Known Use: 1644
REACT Defined for Kids
Definition of react for Students
1 : to act or behave in response to something <Firefighters reacted quickly to the situation.>
2 : to oppose a force or influence Hint: In this sense, react is usually used with against. <Workers reacted against unfair treatment.>
3 : to go through a chemical reaction <Acids react with bases to form salt.>
Seen and Heard
What made you want to look up react? Please tell us where you read or heard it (including the quote, if possible).