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 of react

• 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

Trafford has to react to the movement of the ball, leap up to his left and claw it away from behind him. — Beren Cross, New York Times, 24 July 2026

People on social media reacted to the Observer’s report with outrage at CMPD’s lack of transparency and disbelief in their conclusion, as well as gratitude to the Observer for digging into the subject. — Caitlin McGlade, Charlotte Observer, 24 July 2026

Per the toy company, the electronic sword has multiple play modes that react to movement and music, as well as the user’s own singing. — Tim Lammers, Forbes.com, 23 July 2026

At the time, Hartstone-Rose wasn’t sure why the animals reacted in such different ways. — Jackie Flynn Mogensen, Scientific American, 23 July 2026

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

• act
• backed
• blacked
• bract
• cracked
• fact
• hacked
• jacked
• lacked
• packed
• pact
• racked

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