Definition of react in English:

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Pronunciation: /rēˈakt/


[no object]
1Respond or behave in a particular way in response to something: he reacted angrily to the news of his dismissal the market reacted by falling a further 3.1%
More example sentences
  • Rail passengers have reacted angrily to news that fares are set to rise.
  • All my three daughters react differently to stress.
  • One reason is that financial markets react quickly to policy changes.
behave, act, take it, conduct oneself;
respond, reply, answer
rebel against, oppose, rise up against
1.1 (react against) Respond with hostility, opposition, or a contrary course of action to: they reacted against the elite art music of their time
More example sentences
  • Workers reacted against the outrageous contract demands of the company, voting by an overwhelming 48 to 3 for strike action.
  • How do we react against such violence and war in our time?
  • Third, many people in the younger generation, under age 30 or so, are reacting against the culture of divorce.
1.2(Of a person) suffer from adverse physiological effects after ingesting, breathing, or touching a substance: many babies react to soy-based formulas
More example sentences
  • Therefore you can suddenly react to a substance you may have come in contact with many times before.
  • Why do some members of a family react to environmental substances and develop asthma, while others do not?
  • Our findings indicate that children at risk for atopy react sensitively to chemical substances that originate from passive smoking.
1.3 Chemistry & Physics Interact and undergo a chemical or physical change: the sulfur in the coal reacts with the limestone during combustion
More example sentences
  • When base is added, it reacts with hydronium ion to decrease its concentration, thereby stressing the system.
  • In these reactions the ozone reacts with nitric oxide to produce nitrogen dioxide.
  • Direct sensing mechanisms might involve proteins or ligands that bind or react with oxygen.
1.4 [with object] Chemistry Cause (a substance) to undergo a change by interacting with another substance.
Example sentences
  • These materials are reacted with sulfuric acid, then neutralized, and converted to a salt.
  • Organic sulfates are esters and are formed by reacting an alcohol with cold sulfuric acid or by the reaction of sulfuric acid with a double bond in an alkene.
  • Many alkyl halides, alcohols, or alkenes can be reacted with benzene in the presence of certain catalysts to give an alkyl benzene.
1.5 Stock Market (Of stock prices) fall or rise in reaction to events, developments, etc.
Example sentences
  • Edging down a bit from record highs, but maybe not for long, oil prices react to events in Iraq.
  • The stock price is reacting, up some 50 percent to $15 a share since Payne took charge.
  • Just how will bond markets and stock markets react to the anticipated rise in US interest rates?


Mid 17th century: from re- (expressing intensive force or reversal) + act, originally suggested by medieval Latin react- 'done again', from the verb reagere.

For editors and proofreaders

Syllabification: re·act

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