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

But instead, Crudup had the exact opposite reaction. —Emily Cegielski, Flow Space, 9 Mar. 2025

The model essentially told me that this plan has, in fact, brought about jealous reactions abroad. —John Werner, Forbes, 9 Mar. 2025

But, when a second death beset Lilian’s life, Dr. Fenton’s reaction took her by surprise. —Yiyun Li, The New Yorker, 9 Mar. 2025

What was the public’s reaction to the Notorious B.I.G.’s death? —Skyler Trepel, People.com, 9 Mar. 2025

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

Rhymes for reaction

• abstraction
• attraction
• compaction
• contraction
• detraction
• diffraction
• distraction
• exaction
• extraction
• impaction
• inaction
• infraction

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