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
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
There may be questions about temperament given his bans for reactions against Ipswich Town and Bournemouth, and his work off the ball at Wolves left some staff wanting more.
—
Laurie Whitwell, New York Times, 1 June 2025
Imagine the pressure of having to constantly see around the proverbial corner, while knowing full well the brutal market reaction that awaits after the inevitable mistake.
—John Tamny, Forbes.com, 1 June 2025
It's thought that around 60 percent of people with shellfish allergies experience their first reaction as adults, according to the charity Food Allergy Research and Education.
—Alyce Collins, MSNBC Newsweek, 31 May 2025
Professional gamers tend to appreciate the lack of tactility in linear switches, as any physical impedance increases input lag between the action (pressing a key) and the reaction (your character moving, for example).
—Francisco Lahoz, PC Magazine, 31 May 2025
See All Example Sentences for reaction
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Laurie Whitwell, New York Times, 1 June 2025
Imagine the pressure of having to constantly see around the proverbial corner, while knowing full well the brutal market reaction that awaits after the inevitable mistake.
—John Tamny, Forbes.com, 1 June 2025
It's thought that around 60 percent of people with shellfish allergies experience their first reaction as adults, according to the charity Food Allergy Research and Education.
—Alyce Collins, MSNBC Newsweek, 31 May 2025
Professional gamers tend to appreciate the lack of tactility in linear switches, as any physical impedance increases input lag between the action (pressing a key) and the reaction (your character moving, for example).
—Francisco Lahoz, PC Magazine, 31 May 2025
See All Example Sentences for reaction
Cite this Entry
“Reaction.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/reaction. Accessed 6 Jun. 2025.
Copy CitationKids 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
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