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reaction

noun re·ac·tion \rē-ˈak-shən\

: 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

reactions : the ability to act and move quickly in order to avoid sudden danger

Full Definition of REACTION

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

: 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>

: 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 infective 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

: the force that a body subjected to the action of a force from another body exerts in the opposite direction

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

See reaction defined for English-language learners

See reaction defined for kids

First Known Use of REACTION

circa 1611

Related to REACTION

Synonyms: answer, reply, response, take

Rhymes with REACTION

abstraction, attraction, bolt-action, class action, compaction, contraction, cross action, detraction, diffraction, distraction, exaction, extraction, impaction, inaction, infraction, job action, live-action, olfaction, protraction, redaction, refraction, retraction, stop-action, subtraction, transaction

REACTION Defined for Kids

reaction

noun re·ac·tion \rē-ˈak-shən\

Definition of REACTION for Kids

: behavior or attitude in response to something <What was your reaction to the news?>

: a response of the body to a stimulus <He had an allergic reaction to peanuts.>

: a chemical change that is brought about by the action of one substance on another and results in a new substance being formed

Medical Dictionary

reaction

noun re·ac·tion \rē-ˈak-shən\

Medical Definition of REACTION

: the act or process or an instance of reacting

: 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 infective 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

: the force that a body subjected to the action of a force from another body exerts in the opposite direction

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