Definition of "Reaction" :

noun: doing something in opposition to another way of doing it that you don't like

"His style of painting was a reaction against cubism."

noun: a bodily process occurring due to the effect of some antecedent stimulus or agent

"A bad reaction to the medicine."

noun: an idea evoked by some experience

"His reaction to the news was to start planning what to do."

noun: extreme conservatism in political or social matters

"The forces of reaction carried the election."

noun: a response that reveals a person's feelings or attitude

"He was pleased by the audience's reaction to his performance."

noun: (mechanics) the equal and opposite force that is produced when any force is applied to a body

"Every action has an equal and opposite reaction."

noun: (chemistry) a process in which one or more substances are changed into others

"There was a chemical reaction of the lime with the ground water."