react

verb

re·​act rē-ˈakt 

reacted; reacting; reacts

intransitive verb

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

transitive verb

: to cause to react

Synonyms

• respond

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.

Recent Examples on the Web

So while cells in a younger person (that were continuously exposed to estrogen prior to HRT) might benefit from a fresh influx of estrogen, ones that had a break from that estrogen bath might react negatively to it. —Erica Sloan, SELF, 15 Sep. 2025

Last week, a video of Hasan Piker reacting to the sight of Charlie Kirk getting shot during a discussion at Utah Valley University on Wednesday quickly accumulated millions of views. —Spencer Kornhaber, The Atlantic, 15 Sep. 2025

Fans took to the comments to react, with many praising them both for their humor. —Liza Esquibias, PEOPLE, 15 Sep. 2025

Rainwater reacts with carbon dioxide in the air and becomes slightly acidic, wearing away at rock exposed on the Earth’s surface. —Peter Brannen, Quanta Magazine, 15 Sep. 2025

Word History

Etymology

New Latin reactus, past participle of reagere, from Latin re- + agere to act — more at agent

First Known Use

1644, in the meaning defined at intransitive sense 1

Phrases Containing react

• react against

Rhymes for react

• abstract
• attacked
• attract
• contact
• contract
• detract
• distract
• enact
• exact
• extract
• hijacked
• impact

Kids Definition

react

verb

re·​act rē-ˈakt 

1

: to act or behave in response (as to stimulation or an influence)

the colonists reacted to the tax by boycotting tea

2

: to oppose a force or influence

—usually used with against

reacted against their unfair treatment

3

: to go through or cause to go through a chemical reaction

Medical Definition

react

intransitive verb

re·​act rē-ˈakt 

1

: to respond to a stimulus

2

: to undergo chemical reaction

transitive verb

: to cause to react