Longman Dictionary of Contemporary English homepage

react

 verb
     
Related topics: Chemistry, Illness and Disability
re‧act S3 W3 [intransitive]
1

behaviour/feelings

to behave in a particular way or show a particular emotion because of something that has happened or been said [↪ respond]
react to
How did Wilson react to your idea?
He reacted angrily to the suggestion that he had lied.
She reacted very badly (=was very upset) when her parents split up.
You have to react quickly to circumstances.
react by doing something
The government reacted by declaring all strikes illegal.
➔ overreact
2

chemicals

technicalHC if a chemical substance reacts, it changes when it is mixed with another chemical substance
react with
The calcium reacts with sulphur in the atmosphere.
3

prices

if prices or financial markets react to something that happens, they increase or decrease in value because of it
react to
Oil prices reacted sharply (=reacted a lot) to news of the crisis in the Middle East.
The market reacted favourably to the announcement.
4

become ill

MI to become ill when a chemical or drug goes into your body, or when you eat a particular kind of food [↪ respond]
react to
Quite a lot of children react badly to antibiotics.

react against something

phrasal verb
to show that you dislike someone else's ideas or ways of doing something, by deliberately doing the opposite:
He reacted strongly against his religious upbringing.
Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.
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