1. a response to something that has happened or been said
2. a process in which substances combine or break apart to form new chemical compounds
Usage: chemistry
3. an instance of the body responding badly to a drug, food, or other substance
Usage: medical

Examples

• Her reaction to the news was one of complete surprise.
• The crowd’s reaction to the performance was overwhelmingly positive.
• The chemical reaction produced a bright flash of light.
• He had an allergic reaction to the medication.
• The mixing of acids and bases creates a neutralization reaction.
• She experienced a severe reaction to the shellfish.
• The political reaction against the new policies was swift.