reaction

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

Definition of reaction

1a : 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
5a(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

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Synonyms for reaction

Synonyms

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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.
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Recent Examples on the Web There is always a member of Kiwibot’s staff within three minutes reaction time of a robot, according to the company. Arlene Borenstein-zuluaga, sun-sentinel.com, 4 June 2021 But Senate Appropriations leaders in both parties were cool to the House proposal, which included a quick reaction force to respond to crises and retractable fencing, along with money for hiring more officers and equipment upgrade. Manu Raju, CNN, 3 June 2021 Alcohol can blur judgment, reaction time and abilities, and its effects can be amplified by time in the sun. Laura Schulte, Milwaukee Journal Sentinel, 28 May 2021 Heightened speeds tend to reduce available reaction time and increase the chances of a car crash. Lance Eliot, Forbes, 26 May 2021 American military officials have discussed keeping troops in neighboring countries to maintain a reaction force to go after terrorist threats that might arise in Afghanistan from groups such as Al Qaeda or the Islamic State group. BostonGlobe.com, 25 May 2021 Against Indiana, despite a solid reaction time, Oweh couldn’t convert his strength into power quickly enough, and Bedford washed him out on a short Hoosiers touchdown run. Jonas Shaffer, baltimoresun.com, 25 May 2021 American military officials have discussed keeping troops in neighboring countries to maintain a reaction force to go after terrorist threats that might arise in Afghanistan from groups such as Al Qaeda or the Islamic State. New York Times, 25 May 2021 In addition to providing funding for fencing and making improvements to secure windows and doors, the measure also creates a new quick reaction force of the D.C. National Guard to respond to threats to the Capitol. Melissa Quinn, CBS News, 23 May 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'reaction.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of reaction

1585, in the meaning defined at sense 1a

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Time Traveler for reaction

Time Traveler

The first known use of reaction was in 1585

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Statistics for reaction

Last Updated

7 Jun 2021

Cite this Entry

“Reaction.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/reaction. Accessed 15 Jun. 2021.

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More Definitions for reaction

reaction

noun

English Language Learners Definition of reaction

: the way someone acts or feels in response to something that happens, is said, etc.
: an action or attitude that shows disagreement with or disapproval of someone or something
: the ability to act and move quickly in order to avoid sudden danger

reaction

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

Kids Definition of reaction

1 : behavior or attitude in response to something What was your reaction to the news?
2 : a response of the body to a stimulus He had an allergic reaction to peanuts.
3 : a chemical change that is brought about by the action of one substance on another and results in a new substance being formed

reaction

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

Medical Definition of reaction

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
4a(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

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