reaction

(noun) (chemistry) a process in which one or more substances are changed into others. Synonyms: chemical reaction. Example: "There was a chemical reaction of the lime with the ground water."

(noun) an idea evoked by some experience. Example: "His reaction to the news was to start planning what to do."

(noun) a bodily process occurring due to the effect of some antecedent stimulus or agent. Synonyms: response. Examples: "A bad reaction to the medicine." "His responses have slowed with age."

(noun) (mechanics) the equal and opposite force that is produced when any force is applied to a body. Example: "Every action has an equal and opposite reaction."

(noun) a response that reveals a person's feelings or attitude. Examples: "He was pleased by the audience's reaction to his performance." "John feared his mother's reaction when she saw the broken lamp."

(noun) extreme conservatism in political or social matters. Example: "The forces of reaction carried the election."

(noun) doing something in opposition to another way of doing it that you don't like. Example: "His style of painting was a reaction against cubism."