Definition of react in English:

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Pronunciation: /rɪˈakt/


[no object]
1Act in response to something; respond in a particular way: 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, proceed;
respond, reply, answer;
rare comport oneself
rebel against, oppose, revolt against, rise up against
1.1 (react against) Respond with hostility 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.
1.2Suffer 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 Stock Market (Of share prices) fall after rising: the shares reacted to 222p before rallying to 228p
More 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?
2 Chemistry & Physics Interact and undergo a chemical or physical change: the sulphur 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.
2.1 [with object] Cause (a substance) to undergo a chemical or physical change by interacting with another substance: in the new process the ammonia will be reacted with oxygen
More 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.


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

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