Definition of reaction in English:



  • 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’
    • ‘Fifth, anger can be an immediate reaction to an isolated event or it can be a response after numerous events.’
    • ‘And for an immediate reaction to today's events I think we can speak to Tom Hilton.’
    • ‘The only people who usually benefit from a knee-jerk emotional reaction to a security event are the vendors.’
    • ‘He acknowledged that he had an immediate gut reaction to government requests for the media to withhold information.’
    • ‘Are you surprised by the reaction of your fans?’
    • ‘The market's reaction was swift and brutal.’
    • ‘Describing her mother's reaction to the news, Harrold said she was unable to face even her closest friends.’
    • ‘I accept full responsibility for my reaction to a bad situation.’
    • ‘The violence of Violet's reaction had not surprised her, indeed, she was rather pleased by it.’
    • ‘We are appreciative of the Australian government's reaction to the situation.’
    • ‘Yet the fear of this technical underworld has provoked a knee-jerk reaction.’
    • ‘We also observe a positive market reaction to the announcements of relocations involving corporate headquarters and plants.’
    • ‘Of course, that explained Mother's reaction to the news and her respectfully mournful look.’
    • ‘He said he has been surprised by the positive reaction from the public.’
    • ‘And with little change in Fed thinking, the financial markets' reaction was muted.’
    • ‘However, people have very different mental responses to the body's natural reaction to a stressful situation.’
    • ‘Negative emotional reactions are often caused by stress.’
    • ‘The mention of Thomas provoked an immediate reaction from Becky as the Shopkeeper knew it would.’
    • ‘We test whether the market's reaction to such announcements differs among different types of units relocated.’
    • ‘We need to stop worrying about what others think of us and make pictures that elicit a gut reaction.’
    1. 1.1reactions A person's ability to respond physically and mentally to external stimuli.
      ‘a skilled driver with quick 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.’
      • ‘The drink he had had would have affected his judgement, ability to ride and reactions.’
      • ‘Thus, we consider that birds actually reacted to both stimuli, but reactions were probably weaker than tests performed the previous year.’
      • ‘Likewise, neuroticism may be linked not with stronger reactions to negative stimuli, but with weaker reactions to positive stimuli.’
    2. 1.2 An adverse physiological response to a substance that has been breathed in, ingested, or touched.
      ‘such allergic reactions as hay fever and asthma’
      • ‘Vitamin B 1 may cause a hypersensitivity reaction or dermatitis.’
      • ‘Rarely, skin tests can produce a severe, immediate allergic reaction.’
      • ‘The mechanism for these adverse muscle reactions is unknown.’
      • ‘Other adverse effects of ticlopidine include neutropenia, adverse skin reactions and gastrointestinal side effects.’
      • ‘Rock found that exposure to dogs increased levels of cytokines, chemicals that dampen the body's reactions to allergens.’
      • ‘One risk of any such procedure would be the small possibility of an allergic reaction to the anesthetic used.’
      • ‘Vaccinia immune globulin is a first-line therapy for certain adverse reactions to smallpox vaccine.’
      • ‘Hypersensitivity reactions have also occurred with lamotrigine therapy; some reactions have been fatal or life-threatening.’
      • ‘Anaphylactic reactions have been seen most often after multiple administrations of thiamine.’
      • ‘Pharmacological and therapeutic measures also may be applied to limit adverse physiological reactions to GMA.’
      • ‘"Each antibiotic medicine can cause a strong adverse drug reaction.’
      • ‘Aside from mild gastrointestinal distress and allergic reactions, side effects are rare, and serious toxicity rarely has been reported.’
      • ‘In the realm of immunology, substances that cause immune responses or allergic reactions are known as antigens.’
      • ‘If you don't have an adverse reaction, the allergen dose is increased each time you receive a shot.’
      • ‘If major adverse reactions occur, the regimen, or the offending drug, if identified, must be stopped.’
      • ‘Twenty-five patients experienced adverse drug reactions, but only 12 of them needed drug modifications.’
      • ‘Increased awareness of adverse drug reactions can assist the clinician in differential diagnosis of medical problems and events.’
      • ‘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.’
      • ‘Patients with a known anaphylactic hypersensitivity reaction to eggs should not be vaccinated.’
    3. 1.3 A 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’
      • ‘This is as much a critical reaction against contemporary Hollywood as it is an attempt to capture early-Fifties America.’
      • ‘But we're now seeing a reaction against mass production in the renaissance of organic farming and farmers' markets.’
      • ‘Was this a reaction against this supermarket/microwave culture?’
      • ‘Europhobia seems to be more a reaction against anti-Americanism and its theoretical foundations.’
      • ‘And if the public has a big reaction against something, the story's going to stay for a while.’
      • ‘It is a reaction against modern R & B, which is neither drearily excessive nor underachieving.’
      • ‘But in general there was a strong reaction against the excesses of the previous age.’
      • ‘In the film, Richard goes native as a reaction against the West.’
      • ‘The reaction against raves reflects familiar anxieties about what the kids are up to, especially when it comes to sex.’
      • ‘What's driving the British reaction against Guantanamo Bay?’
      • ‘The rise of conservative views, clubs, and newspapers is a direct reaction against being told how to think.’
      • ‘The reaction against the neo-brutalism of the 1960s and 1970s was to embrace safe conformism instead.’
      • ‘There was then a reaction against these positions.’
      • ‘And in all its forms, even on the conservative Right, it is a reaction against the Enlightenment and is thus essentially new.’
      • ‘So a book Cain wrote as a reaction against his crime novellas became a combination of thriller and woman's picture - film noir.’
      • ‘It is heartening to see a reaction against modern society's safety-first attitude towards child-rearing.’
      • ‘I think this tendency is a reaction against previous generations' parenting styles.’
      • ‘Mawo started in January of 2002 as a reaction against aggressive war behavior of the United States.’
      • ‘The World Bank was actually born in this era of state-led development - it was the Keynesian reaction against the free market.’
      • ‘But among the younger generation there has been a reaction against the positivist and analytical traditions.’
      backlash, counteraction, recoil
      View synonyms
    4. 1.4mass noun Opposition to political or social progress or reform.
      ‘the institution is under threat from the forces of reaction’
      • ‘Today, the Labour Party is a bastion of political reaction.’
      • ‘When you talk about working in a rights mode there is always the element of reaction and pressure.’
      • ‘This process of social and political reaction cannot be adequately explained as the result of the evil intentions of one or another president.’
      • ‘The White House agenda of militarism and social reaction is not some accident, nor is it merely the whim of certain right-wing individuals.’
      • ‘The mood of the broad masses is quite at odds with the creed of avarice and social reaction that animates the incoming government.’
      • ‘The Catholic church may well be a force for intolerance and reaction.’
      • ‘American politics has assumed the form of a sweeping social reaction, aimed at overturning the reformist legacy of the New Deal.’
      • ‘He was to become a bookseller and publisher as well as the owner and editor of the Political Register, in which he launched shattering onslaughts against the forces of reaction.’
      • ‘To find a social base for its reactionary agenda, big business is invariably forced to cultivate political reaction and cultural backwardness.’
      • ‘I think Jack makes a very good point - the forces of extreme reaction are anti-intellectual, but also radical, even if they don't realise it.’
      • ‘The fight against war and social reaction requires a socialist perspective.’
      • ‘In periods of political reaction, innumerable forms of social backwardness, ignorance and stupidity come into their own.’
      • ‘The latter had pledged to sweep all traces of Zionism, imperialism and the forces of reaction in the Arab world.’
      • ‘Ngugi was a professor of English literature at the University of Nairobi until the forces of reaction forced him to flee from Kenya in 1982.’
      • ‘There is no shortcut in the struggle against imperialist war and social reaction.’
      • ‘Such a position ignores the real roots of militarism, war and social reaction - the crisis of American and world capitalism.’
      • ‘It is bound up entirely with the underlying program of militarism abroad and social reaction at home.’
      • ‘It is no coincidence that this development has occurred during a period of deepening social and political reaction.’
      • ‘The forces of reaction in Europe rallied against what they took to be the International and all its works.’
      • ‘It was the forces of reaction which were most prominent and most successful in the 1960s.’
      conservatism, ultra-conservatism, the right, the right wing, the extreme right
      View synonyms
  • 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’
    • ‘Equivalents can be used to simplify balancing chemical equations for many reactions.’
    • ‘Exothermic reactions involve the production of energy which is given to the surrounding environment as heat.’
    • ‘Three randomly picked clones from each PCR reaction were eventually sequenced.’
    • ‘Such " ribozymes " are often used to catalyze reactions involving deoxyribonucleic acid or RNA.’
    • ‘Indeed, electrical currents could lead to a potential drop and to heating and catalysis of undesirable electrochemical reactions.’
    • ‘The rate of a photolysis reaction is a first-order process.’
    • ‘The chemical equations for some reactions may have a lone reactant or a single product.’
    • ‘One of the primary methods of qualitative analysis involves precipitation reactions.’
    • ‘There are many important industrial processes that use electrophilic reactions.’
    • ‘Chemists study these organisms because they are able to perform chemical reactions under extreme conditions.’
    • ‘More to the point, it has facilitated many reactions that depend upon acetic acid as a reagent or solvent.’
    • ‘Ozone is produced when sunlight triggers chemical reactions involving reactive hydrocarbons and nitrogen oxides.’
    • ‘Alkylation reactions are reactions where an alkyl group is introduced into a molecule.’
    • ‘These materials are based on the polymerization reaction of a diol with a diisocyanate.’
    • ‘By contrast, making Kevlar involves a complex series of organic reactions in hot sulphuric acid at high pressures.’
    • ‘Many of these vinyl compounds are made by the reaction of acetylene with electrophiles.’
    • ‘Acid reactions are also used in organic synthesis reactions for making polymers, vitamin supplements, and other everyday consumer products.’
    • ‘Filler metal is obtained from an exothermic reaction between iron oxide and aluminum.’
    • ‘Zeolites can soak up liquid or gas molecules and also catalyze chemical reactions.’
    • ‘It is formed from the reaction of nitric oxide with superoxide, and produces carbonyls on proteins.’
    1. 2.1Physics An analogous transformation of atomic nuclei or other particles.
      ‘reactions between photons and electrically charged atomic particles’
      • ‘Nucleophilic substitution reactions can be either unimolecular or bimolecular.’
      • ‘Cold fusion is the term proposed to describe controlled nuclear fusion reactions occurring at or near room temperature.’
      • ‘It studies the structure of nuclei, and their reactions and interactions.’
      • ‘Furthermore, the compound nuclei produced in cold-fusion reactions contain a relatively small number of neutrons.’
      • ‘They're produced during nuclear fusion, the reaction that lights the sun and other stars.’
  • 3Physics
    mass noun A force exerted in opposition to an applied force.

    ‘the law of action and reaction’
    • ‘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.’


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