CAUSED BY SOMETHING [C, U] › 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] › 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 which happens when two substances are put together: a chemical reaction → See also chain reaction