Definition of reaction noun from the Oxford Advanced American Dictionary

        

    reaction

     noun
    noun
    NAmE//riˈækʃn//
     
     
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  1. 1[countable, uncountable] reaction (to somebody/something) what you do, say, or think as a result of something that has happened What was his reaction to the news? My immediate reaction was one of shock. A spokesman said the changes were not in reaction to the company's recent losses. There has been a mixed reaction to her appointment as director. The decision provoked an angry reaction from local residents. I tried shaking him but there was no reaction.
  2. change in attitudes
  3. 2[countable, usually singular, uncountable] reaction (against something) a change in people's attitudes or behavior caused by disapproval of the attitudes, etc. of the past The return to traditional family values is a reaction against the permissiveness of recent decades.
  4. to drugs
  5. 3[countable, uncountable] a response by the body, usually a bad one, to a drug, chemical substance, etc. to have an allergic reaction to a drug
  6. to danger
  7. 4 reactions [plural] the ability to move, or do something, quickly in response to something, especially if in danger a skilled driver with quick reactions
  8. against progress
  9. 5[uncountable] opposition to social or political progress or change The forces of reaction made change difficult.
  10. science
  11. 6[countable, uncountable] (chemistry) a chemical change produced by two or more substances acting on each other a chemical/nuclear reaction see also chain reaction
  12. 7 [uncountable, countable] (physics) a force shown by something in response to another force, which is of equal strength and acts in the opposite direction Action and reaction are equal and opposite.
See the Oxford Advanced Learner's Dictionary entry: reaction