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

The product formulas still react to skin’s pH levels for bespoke color and shine, but the new iteration has two new finishes, Sparkly and Glaze, in addition to the original Juicy finish. —Jennifer Weil, Footwear News, 22 Dec. 2025

Zadorov had already been tossed out for reacting to Dylan Cozens kneeing him. —Steve Conroy, Boston Herald, 22 Dec. 2025

She’s been reacting to her environment since the trauma of the volcano. —David Canfield, HollywoodReporter, 22 Dec. 2025

Don't wrap silver in newspapers or use rubber bands since these items contain chemicals that can react with silver. —Daley Quinn, Southern Living, 21 Dec. 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