Responds to something that happens; shows a response or change in behavior because of an event or stimulus.
From Latin 're-' (back) and 'agere' (to do or act). Originally meant to do something in response, evolving from chemistry terminology.
The word 'react' comes from chemistry—where chemicals 'react' to other chemicals—but we borrowed the term to describe people's emotional responses too, which is why both meanings use the same word.
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