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 their 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
Hobbs disconnected the state's voter database from the site and sent a quick reaction team to help fix whatever gap the foreign users had slipped through.
—
Sarah D. Wire,
USA Today,
28 June 2026
Ironically, my reaction to a previous illuminated tire light may have lulled me into complacency when that light returned months later.
—
Doug Turnbull,
AJC.com,
28 June 2026
Handle power dynamics well by stating needs and listening for fears beneath reactions.
—
Tarot.com,
Sun Sentinel,
28 June 2026
The reactions, though, can be complicated.
—
Dom Amore,
Hartford Courant,
27 June 2026
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.
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Sarah D. Wire,
USA Today,
28 June 2026
Ironically, my reaction to a previous illuminated tire light may have lulled me into complacency when that light returned months later.
—
Doug Turnbull,
AJC.com,
28 June 2026
Handle power dynamics well by stating needs and listening for fears beneath reactions.
—
Tarot.com,
Sun Sentinel,
28 June 2026
The reactions, though, can be complicated.
—
Dom Amore,
Hartford Courant,
27 June 2026
See All Example Sentences for reaction
Cite this Entry
“Reaction.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/reaction. Accessed 30 Jun. 2026.
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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