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

Other staff members react with shock and concern after the fall, the video shows. — Marlene Lenthang, NBC news, 9 July 2026

These cracks were filled by the lime clasts that reacted with salt or rainwater to recrystallize. — Encyclopedia Britannica, 9 July 2026

The 44-year-old Millete, who has been in custody since October 2021, did not appear to react to the verdict as it was announced in a crowded third-floor courtroom. — Alex Riggins, San Diego Union-Tribune, 9 July 2026

In October 2020, Burnham happened to be holding a news conference on live TV, when an aide passed him a phone with news of another lockdown — and the mayor reacted angrily, lashing out at the central government. — Lauren Frayer, NPR, 9 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