The meaning of REACTION is the act or process or an instance of reacting. How to use reaction in a sentence.

A reaction is an action taken in response to something. If you're telling your parents that you want to move out, you'll see by their reaction that they're sad about it.

Definition of reaction noun in Oxford Advanced American Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

Usage: Reaction is used to refer both to an instant response (her reaction was one of amazement) and to a considered response in the form of a statement (the Minister gave his reaction to the court's …

Reaction is used to refer both to an instant response (her reaction was one of amazement) and to a considered response in the form of a statement (the Minister gave his reaction to the court's decision).

Your reaction to something that has happened or something that you have experienced is what you feel, say, or do because of it.

reaction noun (CHANGE) a change in the way people behave or think because they do not agree with the way people behaved or thought in the past:

Jan 20, 2026 · Noun reaction (plural reactions) An action or statement in response to a stimulus or other event.

Reaction definition: A reverse or opposing action.

Therefore, 'reaction' essentially means 'to act or respond back.' This etymology captures the essence of what a reaction is - a response or behavior that occurs as a result of a stimulus, event, or situation.