Definition of reaction in English:

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Pronunciation: /rɪˈakʃ(ə)n/


1Something done, felt, or thought in response to a situation or event: my immediate reaction was one of relief [mass noun]: prices fell in reaction to intense competition
More example sentences
  • And for an immediate reaction to today's events I think we can speak to Tom Hilton.
  • Fifth, anger can be an immediate reaction to an isolated event or it can be a response after numerous events.
  • I accept full responsibility for my reaction to a bad situation.
answer, reply, rejoinder, retort, riposte;
informal comeback
1.1 (reactions) A person’s ability to respond physically and mentally to external stimuli: a skilled driver with quick reactions
More example sentences
  • The drink he had had would have affected his judgement, ability to ride and reactions.
  • The driver's reactions and abilities wouldn't enter into it.
  • You will soon develop quicker reactions and a sixth sense for when someone is going to do something unorthodox.
1.2An adverse physiological response to a substance that has been breathed in, ingested, or touched: such allergic reactions as hay fever and asthma
More example sentences
  • Other adverse effects of ticlopidine include neutropenia, adverse skin reactions and gastrointestinal side effects.
  • Other measures that should be performed to minimize the risk of adverse reactions to allergen immunotherapy are listed in Table 6.
  • Patients were reassessed on day 4 of therapy for clinical and laboratory responses and for adverse reactions to the medication.
1.3A mode of thinking or behaving that is deliberately different from previous modes of thought and behaviour: the work of these painters was a reaction against Fauvism
More example sentences
  • Mawo started in January of 2002 as a reaction against aggressive war behavior of the United States.
  • I think this tendency is a reaction against previous generations' parenting styles.
  • But among the younger generation there has been a reaction against the positivist and analytical traditions.
backlash, counteraction, recoil
1.4 [mass noun] Opposition to political or social progress or reform: the institution is under threat from the forces of reaction
More example sentences
  • It is no coincidence that this development has occurred during a period of deepening social and political reaction.
  • This process of social and political reaction cannot be adequately explained as the result of the evil intentions of one or another president.
  • American politics has assumed the form of a sweeping social reaction, aimed at overturning the reformist legacy of the New Deal.
conservatism, ultra-conservatism, the right, the right wing, the extreme right;
counter-revolution, revanchism
2A chemical process in which substances act mutually on each other and are changed into different substances, or one substance changes into other substances: a chemical reaction caused by a build-up of particular sodium salts
More example sentences
  • There are many important industrial processes that use electrophilic reactions.
  • By contrast, making Kevlar involves a complex series of organic reactions in hot sulphuric acid at high pressures.
  • More to the point, it has facilitated many reactions that depend upon acetic acid as a reagent or solvent.
2.1 Physics An analogous transformation of atomic nuclei or other particles: reactions between photons and electrically charged atomic particles
More example sentences
  • Furthermore, the compound nuclei produced in cold-fusion reactions contain a relatively small number of neutrons.
  • It studies the structure of nuclei, and their reactions and interactions.
  • They're produced during nuclear fusion, the reaction that lights the sun and other stars.
3 [mass noun] Physics A force exerted in opposition to an applied force: the law of action and reaction
More example sentences
  • In response to the motion, the elastic reaction force exerted on the site by the substrate starts to rise.
  • Newton's third law states that for every action there's an equal and opposite reaction.
  • At the same time, the centrifugal forces of interest and reaction caused local people to reconceive the boundaries of their nation.



Pronunciation: /rɪˈakʃ(ə)nɪst/
noun& adjective
Example sentences
  • In every war it was the opportune time for the reactionist and commercial vulture to do his dirty work in the name of patriotism.
  • They are using their reactionist tactics to try and scare people away from real issues.


Mid 17th century: from react + -ion, originally suggested by medieval Latin reactio(n-), from react- 'done again' (see react).

For editors and proofreaders

Line breaks: re|ac¦tion

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