reaction

noun

re·​ac·​tion rē-ˈak-shən 

1

a

: the act or process or an instance of reacting

b

: resistance or opposition to a force, influence, or movement

especially : tendency toward a former and usually outmoded political or social order or policy

2

: a response to some treatment, situation, or stimulus

her stunned reaction to the news

also : such a response expressed verbally

critical reaction to the play

3

: bodily response to or activity aroused by a stimulus:

a

: an action induced by vital resistance to another action

especially : the response of tissues to a foreign substance (such as an antigen or infectious agent)

b

: depression or exhaustion due to excessive exertion or stimulation

c

: heightened activity and overaction succeeding depression or shock

d

: a mental or emotional disorder forming an individual's response to his or her life situation

4

: the force that a body subjected to the action of a force from another body exerts in the opposite direction

5

a(1)

: chemical transformation or change : the interaction of chemical entities

(2)

: the state resulting from such a reaction

b

: a process involving change in atomic nuclei

Synonyms

• answer
• reply
• response
• take

Examples of reaction in a Sentence

Their reaction to the news was positive.

When I told him what happened, his immediate reaction was one of shock.

The announcement produced an angry reaction from most of the people at the meeting.

My first reaction when I met him was not to trust him.

There hasn't yet been much reaction to the announcement.

There has been strong reaction against the government's policies.

A good driver has quick reactions.

The speed of his reactions saved his life.

Recent Examples on the Web

For a scene on The Racer roller coaster, a camera was temporarily mounted to the front of the car, facing backward for a reaction shot. —Jeff Suess, The Enquirer, 19 Apr. 2024

The school board’s defiant reaction signals that conservative local officials are willing to challenge the state’s interpretation of the law as well as the state’s overall authority to intervene in local matters of this sort. —Howard Blume, Los Angeles Times, 19 Apr. 2024

According to Padilla, the district discourages students from sharing candy and other food items because of the possibility of an allergic or other type of adverse reaction. —Harriet Ramos, Fort Worth Star-Telegram, 18 Apr. 2024

The reaction scene plays out not with churning pathos but instead like TikToks of people watching Ned Stark meet his surprising fate or videos of fans in a sports bar groaning in unison. —Margaret Lyons, New York Times, 18 Apr. 2024

Its stock fell almost 7% on the Thursday, but Brophy said that the market’s reaction was more a product of its astronomical expectations than any real failures at TSMC. —Dylan Sloan, Fortune, 18 Apr. 2024

Changes to the fictional character were no doubt driven at least in part by the reaction of the real-life Münchhausen. —Rosemary Counter, Smithsonian Magazine, 17 Apr. 2024

My first impression was their live show and the fans’ reaction. —Leena Tailor, Variety, 17 Apr. 2024

As if that weren’t enough, an onboard storage tank captures the water that is the byproduct of the electrochemical reactions in the fuel cell. —IEEE Spectrum, 16 Apr. 2024

Word History

First Known Use

1585, in the meaning defined at sense 1a

Phrases Containing reaction

• alarm reaction
• chain reaction
• chemical reaction
• counter-reaction
• cross-reaction
• dark reaction
• Feulgen reaction
• Hill reaction
• in reaction to
• light reaction
• Maillard reaction
• mixed reaction
• nuclear reaction
• polymerase chain reaction
• reaction gif
• Wassermann reaction

Kids Definition

reaction

noun

re·​ac·​tion rē-ˈak-shən 

1

a

: the act or process or an instance of reacting

our reaction to the news

b

: an action or attitude opposing current political or social forces or ideas

2

: a bodily response to a stimulus

especially : the response of the body to a foreign substance (as a drug)

3

: the force that opposes the action of a force applied to one body by another body

4

a

: chemical transformation or change : the action between atoms or molecules to form one or more new substances

b

: a process involving change in atomic nuclei

Medical Definition

reaction

noun

re·​ac·​tion rē-ˈak-shən 

1

: the act or process or an instance of reacting

2

: bodily response to or activity aroused by a stimulus:

a

: an action induced by vital resistance to another action

especially : the response of tissues to a foreign substance (as an antigen or infectious agent)

b

: depression or exhaustion due to excessive exertion or stimulation

c

: abnormally heightened activity succeeding depression or shock

d

: a mental or emotional disorder forming an individual's response to his or her life situation

3

: the force that a body subjected to the action of a force from another body exerts in the opposite direction

4

a(1)

: chemical transformation or change : the interaction of chemical entities

(2)

: the state resulting from such a reaction

b

: a process involving change in atomic nuclei