Meaning of “reaction” - Learner’s Dictionary

reaction

noun us uk /riˈækʃən/
My initial reaction was one of anger.It's impossible to gauge what her reaction will be.He was clearly rattled by their angry reaction.What is your reaction to these comments?People have had different reactions to the end of the film.
CAUSED BY SOMETHING [ C, U ]

B2 something you say, feel, or do because of something that has happened:

What was his reaction to the news?
reactions mainly UK

the ability to move quickly when something suddenly happens:

Drivers need to have quick reactions.
CHANGE [ no plural ]

a change in the way people behave or think because they do not agree with the way people behaved or thought in the past:

In art, there was a reaction against Realism.
BAD EFFECT [ C ]

B2 an unpleasant feeling or illness caused by something you have eaten or used on your body:

A number of people have had a / bad reaction to this drug.
SUBSTANCES [ C ]

a change that happens when two substances are put together:

a chemical reaction
→ See also chain reaction

(Definition of “reaction” from the Cambridge Learner’s Dictionary © Cambridge University Press)