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

Synonyms for reaction

Synonyms

Visit the Thesaurus for More 

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. See More
Recent Examples on the Web An in-office patch test can identify the specific source(s) of the reaction. Sarah Ban, SELF, 3 Aug. 2022 DeGrom, who has dealt with a stress reaction on his right scapula, has not pitched in the majors in more than a year. New York Times, 28 July 2022 Sidelined all season by a stress reaction in his right scapula, deGrom gave up four runs on a pair of homers and threw 41 of 67 pitches for strikes. Mike Fitzpatrick, ajc, 27 July 2022 Stay strong, and try not to give them the satisfaction of a reaction. Chicago Tribune, 26 July 2022 The 34-year-old hasn’t pitched in the majors since July 7, 2021, sidelined since late in spring training by a stress reaction in his right scapula . . . BostonGlobe.com, 25 July 2022 Tests revealed Chisholm has a stress reaction in his lower back, the Marlins said Friday. John Perrotto, Sun Sentinel, 23 July 2022 Still, fans got a kick out of the relatable reaction. Emily Tannenbaum, Glamour, 22 July 2022 Mets ace Jacob deGrom is coming back after he was sidelined by a stress reaction in his right scapula. Creg Stephenson | Cstephenson@al.com, al, 21 July 2022 See More

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.

First Known Use of reaction

1585, in the meaning defined at sense 1a

Learn More About reaction

Time Traveler for reaction

Time Traveler

The first known use of reaction was in 1585

See more words from the same year

Dictionary Entries Near reaction

reactant

reaction

reactional

See More Nearby Entries 

Statistics for reaction

Last Updated

6 Aug 2022

Cite this Entry

“Reaction.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/reaction. Accessed 11 Aug. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

More Definitions for reaction

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

More from Merriam-Webster on reaction

Nglish: Translation of reaction for Spanish Speakers

Britannica English: Translation of reaction for Arabic Speakers

Britannica.com: Encyclopedia article about reaction

WORD OF THE DAY

Test Your Vocabulary

Words Named After People

  • name tags
  • Namesake of the leotard, Jules Léotard had what profession?
Spell It

Can you spell these 10 commonly misspelled words?

TAKE THE QUIZ
Universal Daily Crossword

A daily challenge for crossword fanatics.

TAKE THE QUIZ
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!