to event/situation
1 [countable, uncountable] reaction (to somebody/something) what you do, say or think as a result of something that has happenedWhat 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. change in attitudes
2 [countable, usually singular, uncountable] reaction (against something) a change in people's attitudes or behaviour caused by disapproval of the attitudes, etc. of the pastThe return to traditional family values is a reaction against the permissiveness of recent decades. to drugs
3 [countable, uncountable] a response by the body, usually a bad one, to a drug, chemical substance, etcto have an allergic reaction to a drug to danger
4 reactions [plural] the ability to move quickly in response to something, especially if in dangera skilled driver with quick reactions science
5 [countable, uncountable] (chemistry) a chemical change produced by two or more substances acting on each othera chemical/nuclear reaction see also chain reaction6 [uncountable, countable] (physics) a force shown by something in response to another force, which is of equal strength and acts in the opposite directionAction and reaction are equal and opposite.
against progress
7 [uncountable] opposition to social or political progress or changeThe forces of reaction made change difficult.
riˈækʃn 
riˈækʃn 