react

verb

re·​act rē-ˈakt 

reacted; reacting; reacts

intransitive verb

1

: to change in response to a stimulus: such as

a

: to act or behave in a certain way in response to a situation, comment, etc.

When I told her what happened, she reacted with anger.

Most people reacted positively to the news.

The firefighters reacted quickly when they heard the alarm.

b

: to be or have a bodily response to something : to be or have a reaction (see reaction sense 3)

the way our bodies react to cold/pain

was not sure how the patient would react to the treatment

2

: to act in opposition to a force or influence

—usually used with against

a group of artists who reacted against convention

3

: to move or tend in a reverse direction

Stock prices reacted strongly after a brief drop.

4

: to exert a reciprocal or counteracting force or influence

—often used with on or upon

… his solitude … reacted on [=had an effect on] his character.

—Henry Adams

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

Huang has said that this system gives his company the flexibility to react to rapid changes in technology and remain agile. — Los Angeles Times, 9 Nov. 2026

Drivers are responsible for being alert and aware of changes, and being able to react when others make mistakes or slow down. — Doug Turnbull, AJC.com, 8 Nov. 2026

Trump will likely use his veto on the removal of tariffs, and then let’s see how Republicans react. — Bob Kustra, Chicago Tribune, 8 Nov. 2026

Lakes react quickly to changes in the environment, so measuring lake color through satellite monitoring can help quantify those changes. — Connie Hanzhang Jin, NPR, 8 Nov. 2026

Word History

Etymology

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

First Known Use

circa 1608, 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