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
The controversial idea to play a domestic league fixture overseas, pushed by La Liga president Javier Tebas to increase Spanish football’s revenues and exposure, attracted completely opposing reactions from the two sides of the Barca-Madrid divide.
—
Dermot Corrigan, New York Times, 25 Oct. 2025
Their focus on grooming and abuse of students comes in reaction to recent reporting by The Capital Times on about 200 cases of such incidents since 2018, including some cases of teachers who were able to later reapply for a license.
—Molly Beck, jsonline.com, 24 Oct. 2025
Costumes and makeup products or peanuts or tree nuts in candies can also trigger severe allergic reactions and rashes.
—Katia Hetter, CNN Money, 24 Oct. 2025
Content creators now use it for just about anything and its appearance often sparks raucous reactions, like in September when a crowd erupted in cheers after an In-N-Out employee called out order number 67.
—Diana Leyva, Nashville Tennessean, 24 Oct. 2025
See All Example Sentences for reaction
Examples are automatically compiled from online sources to
show current usage.
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Dermot Corrigan, New York Times, 25 Oct. 2025
Their focus on grooming and abuse of students comes in reaction to recent reporting by The Capital Times on about 200 cases of such incidents since 2018, including some cases of teachers who were able to later reapply for a license.
—Molly Beck, jsonline.com, 24 Oct. 2025
Costumes and makeup products or peanuts or tree nuts in candies can also trigger severe allergic reactions and rashes.
—Katia Hetter, CNN Money, 24 Oct. 2025
Content creators now use it for just about anything and its appearance often sparks raucous reactions, like in September when a crowd erupted in cheers after an In-N-Out employee called out order number 67.
—Diana Leyva, Nashville Tennessean, 24 Oct. 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 27 Oct. 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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