reaction

noun

re·​ac·​tion rē-ˈak-shən How to pronounce reaction (audio)
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

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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
See earnings reaction history of all stocks Autodesk’s Historical Odds Of Positive Post-Earnings Return Key insights on one-day (1D) post-earnings returns: There are 20 earnings data points noted over the past five years, with 10 positive and 10 negative one-day (1D) returns recorded. Trefis Team, Forbes.com, 20 May 2025 Even sitting in one position too long can trigger a reaction. Ashley Vega, People.com, 20 May 2025 In an age of reaction videos, a 2024 YouTube survey found that 66% of Gen Z Americans spend more time watching content that discusses something than that thing itself. Jacob Feldman, Sportico.com, 20 May 2025 An describes one reaction test where six pairs of dots rotate on a screen in different directions and speeds — some clockwise, counterclockwise, etc. — and some are highlighted at the start. Christopher Cruz, Rolling Stone, 20 May 2025 See All Example Sentences for reaction

Word History

First Known Use

1585, in the meaning defined at sense 1a

Time Traveler
The first known use of reaction was in 1585

Browse Nearby Words

Cite this Entry

“Reaction.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/reaction. Accessed 25 May. 2025.

Kids Definition

reaction

noun
re·​ac·​tion rē-ˈak-shən How to pronounce reaction (audio)
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 How to pronounce reaction (audio)
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

More from Merriam-Webster on reaction

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