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

Related Stories Speaking to Variety on the red carpet at its London Film Festival premiere on Sunday, Garfield — who has been Oscar-nominated twice but never won — reacted humbly to the praise. — Alex Ritman, Variety, 12 Oct. 2026

Chaim Goodman-Strauss, one of the mathematicians behind the hat proof and an outreach mathematician at the National Museum of Mathematics, wrote a preprint reacting to the Chair44 results. — Rachel Crowell, Scientific American, 12 Oct. 2026

Lower inertia can help a robotic arm accelerate and decelerate more readily, potentially improving its ability to react quickly when handling moving objects. — Kaif Shaikh, Interesting Engineering, 10 Oct. 2026

The technique is called closed-loop auditory stimulation, which is a jargony way of saying the device reads what your brain is doing and reacts in the moment. — Hanna Wickes, Fort Worth Star-Telegram, 9 Oct. 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