What does REACTION mean?

noun

1. (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”
2. an idea evoked by some experience“his reaction to the news was to start planning what to do”
3. a bodily process occurring due to the effect of some antecedent stimulus or agent“a bad reaction to the medicine”
4. (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”
5. a response that reveals a person's feelings or attitude“he was pleased by the audience's reaction to his performance”
6. extreme conservatism in political or social matters“the forces of reaction carried the election”
7. doing something in opposition to another way of doing it that you don't like“his style of painting was a reaction against cubism”