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’
    • ‘And for an immediate reaction to today's events I think we can speak to Tom Hilton.’
    • ‘I accept full responsibility for my reaction to a bad situation.’
    • ‘Are you surprised by the reaction of your fans?’
    • ‘Of course, that explained Mother's reaction to the news and her respectfully mournful look.’
    • ‘We are appreciative of the Australian government's reaction to the situation.’
    • ‘We also observe a positive market reaction to the announcements of relocations involving corporate headquarters and plants.’
    • ‘The market's reaction was swift and brutal.’
    • ‘Fifth, anger can be an immediate reaction to an isolated event or it can be a response after numerous events.’
    • ‘We need to stop worrying about what others think of us and make pictures that elicit a gut reaction.’
    • ‘However, people have very different mental responses to the body's natural reaction to a stressful situation.’
    • ‘The violence of Violet's reaction had not surprised her, indeed, she was rather pleased by it.’
    • ‘We test whether the market's reaction to such announcements differs among different types of units relocated.’
    • ‘The only people who usually benefit from a knee-jerk emotional reaction to a security event are the vendors.’
    • ‘And with little change in Fed thinking, the financial markets' reaction was muted.’
    • ‘Yet the fear of this technical underworld has provoked a knee-jerk reaction.’
    • ‘Describing her mother's reaction to the news, Harrold said she was unable to face even her closest friends.’
    • ‘Negative emotional reactions are often caused by stress.’
    • ‘He said he has been surprised by the positive reaction from the public.’
    • ‘The mention of Thomas provoked an immediate reaction from Becky as the Shopkeeper knew it would.’
    • ‘He acknowledged that he had an immediate gut reaction to government requests for the media to withhold information.’
    1. 1.1reactions A person's ability to respond physically and mentally to external stimuli.
      ‘a skilled driver with quick reactions’
      • ‘You will soon develop quicker reactions and a sixth sense for when someone is going to do something unorthodox.’
      • ‘Likewise, neuroticism may be linked not with stronger reactions to negative stimuli, but with weaker reactions to positive stimuli.’
      • ‘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.’
      • ‘The driver's reactions and abilities wouldn't enter into it.’
    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’
      • ‘The mechanism for these adverse muscle reactions is unknown.’
      • ‘If major adverse reactions occur, the regimen, or the offending drug, if identified, must be stopped.’
      • ‘One risk of any such procedure would be the small possibility of an allergic reaction to the anesthetic used.’
      • ‘Pharmacological and therapeutic measures also may be applied to limit adverse physiological reactions to GMA.’
      • ‘Twenty-five patients experienced adverse drug reactions, but only 12 of them needed drug modifications.’
      • ‘Vitamin B 1 may cause a hypersensitivity reaction or dermatitis.’
      • ‘"Each antibiotic medicine can cause a strong adverse drug reaction.’
      • ‘In the realm of immunology, substances that cause immune responses or allergic reactions are known as antigens.’
      • ‘Aside from mild gastrointestinal distress and allergic reactions, side effects are rare, and serious toxicity rarely has been reported.’
      • ‘If you don't have an adverse reaction, the allergen dose is increased each time you receive a shot.’
      • ‘Hypersensitivity reactions have also occurred with lamotrigine therapy; some reactions have been fatal or life-threatening.’
      • ‘Vaccinia immune globulin is a first-line therapy for certain adverse reactions to smallpox vaccine.’
      • ‘Anaphylactic reactions have been seen most often after multiple administrations of thiamine.’
      • ‘Other measures that should be performed to minimize the risk of adverse reactions to allergen immunotherapy are listed in Table 6.’
      • ‘Other adverse effects of ticlopidine include neutropenia, adverse skin reactions and gastrointestinal side effects.’
      • ‘Patients with a known anaphylactic hypersensitivity reaction to eggs should not be vaccinated.’
      • ‘Rarely, skin tests can produce a severe, immediate allergic reaction.’
      • ‘Patients were reassessed on day 4 of therapy for clinical and laboratory responses and for adverse reactions to the medication.’
      • ‘Increased awareness of adverse drug reactions can assist the clinician in differential diagnosis of medical problems and events.’
      • ‘Rock found that exposure to dogs increased levels of cytokines, chemicals that dampen the body's reactions to allergens.’
    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.’
      • ‘There was then a reaction against these positions.’
      • ‘The World Bank was actually born in this era of state-led development - it was the Keynesian reaction against the free market.’
      • ‘But in general there was a strong reaction against the excesses of the previous age.’
      • ‘Europhobia seems to be more a reaction against anti-Americanism and its theoretical foundations.’
      • ‘It is heartening to see a reaction against modern society's safety-first attitude towards child-rearing.’
      • ‘What's driving the British reaction against Guantanamo Bay?’
      • ‘But we're now seeing a reaction against mass production in the renaissance of organic farming and farmers' markets.’
      • ‘In the film, Richard goes native as a reaction against the West.’
      • ‘So a book Cain wrote as a reaction against his crime novellas became a combination of thriller and woman's picture - film noir.’
      • ‘The reaction against raves reflects familiar anxieties about what the kids are up to, especially when it comes to sex.’
      • ‘It is a reaction against modern R & B, which is neither drearily excessive nor underachieving.’
      • ‘The rise of conservative views, clubs, and newspapers is a direct reaction against being told how to think.’
      • ‘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.’
      • ‘And if the public has a big reaction against something, the story's going to stay for a while.’
      • ‘Mawo started in January of 2002 as a reaction against aggressive war behavior of the United States.’
      • ‘And in all its forms, even on the conservative Right, it is a reaction against the Enlightenment and is thus essentially new.’
      • ‘The reaction against the neo-brutalism of the 1960s and 1970s was to embrace safe conformism instead.’
      • ‘Was this a reaction against this supermarket/microwave culture?’
      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’
      • ‘In periods of political reaction, innumerable forms of social backwardness, ignorance and stupidity come into their own.’
      • ‘This process of social and political reaction cannot be adequately explained as the result of the evil intentions of one or another president.’
      • ‘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.’
      • ‘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.’
      • ‘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.’
      • ‘It was the forces of reaction which were most prominent and most successful in the 1960s.’
      • ‘The fight against war and social reaction requires a socialist perspective.’
      • ‘The White House agenda of militarism and social reaction is not some accident, nor is it merely the whim of certain right-wing individuals.’
      • ‘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.’
      • ‘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.’
      • ‘There is no shortcut in the struggle against imperialist war and social reaction.’
      • ‘American politics has assumed the form of a sweeping social reaction, aimed at overturning the reformist legacy of the New Deal.’
      • ‘The latter had pledged to sweep all traces of Zionism, imperialism and the forces of reaction in the Arab world.’
      • ‘Such a position ignores the real roots of militarism, war and social reaction - the crisis of American and world capitalism.’
      • ‘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.’
      • ‘It is bound up entirely with the underlying program of militarism abroad and social reaction at home.’
      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’
    • ‘The rate of a photolysis reaction is a first-order process.’
    • ‘Acid reactions are also used in organic synthesis reactions for making polymers, vitamin supplements, and other everyday consumer products.’
    • ‘By contrast, making Kevlar involves a complex series of organic reactions in hot sulphuric acid at high pressures.’
    • ‘Zeolites can soak up liquid or gas molecules and also catalyze chemical reactions.’
    • ‘Filler metal is obtained from an exothermic reaction between iron oxide and aluminum.’
    • ‘There are many important industrial processes that use electrophilic reactions.’
    • ‘It is formed from the reaction of nitric oxide with superoxide, and produces carbonyls on proteins.’
    • ‘Chemists study these organisms because they are able to perform chemical reactions under extreme conditions.’
    • ‘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.’
    • ‘Ozone is produced when sunlight triggers chemical reactions involving reactive hydrocarbons and nitrogen oxides.’
    • ‘These materials are based on the polymerization reaction of a diol with a diisocyanate.’
    • ‘Many of these vinyl compounds are made by the reaction of acetylene with electrophiles.’
    • ‘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.’
    • ‘More to the point, it has facilitated many reactions that depend upon acetic acid as a reagent or solvent.’
    • ‘One of the primary methods of qualitative analysis involves precipitation reactions.’
    • ‘The chemical equations for some reactions may have a lone reactant or a single product.’
    • ‘Equivalents can be used to simplify balancing chemical equations for many reactions.’
    • ‘Alkylation reactions are reactions where an alkyl group is introduced into a molecule.’
    1. 2.1Physics An analogous transformation of atomic nuclei or other particles.
      ‘reactions between photons and electrically charged atomic particles’
      • ‘They're produced during nuclear fusion, the reaction that lights the sun and other stars.’
      • ‘Cold fusion is the term proposed to describe controlled nuclear fusion reactions occurring at or near room temperature.’
      • ‘Nucleophilic substitution reactions can be either unimolecular or bimolecular.’
      • ‘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.’
  • 3Physics
    mass noun A force exerted in opposition to an applied force.

    ‘the law of action and reaction’
    • ‘At the same time, the centrifugal forces of interest and reaction caused local people to reconceive the boundaries of their nation.’
    • ‘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.’


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