Open English Wordnet
Nouns
(n)chemical reaction, reaction(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” (n)reactionan idea evoked by some experience“his reaction to the news was to start planning what to do” (n)reaction, responsea bodily process occurring due to the effect of some antecedent stimulus or agent“a bad reaction to the medicine”,
“his responses have slowed with age” (n)reaction(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” (n)reactiona response that reveals a person's feelings or attitude“he was pleased by the audience's reaction to his performance”,
“John feared his mother's reaction when she saw the broken lamp” (n)reactionextreme conservatism in political or social matters“the forces of reaction carried the election” (n)reactiondoing something in opposition to another way of doing it that you don't like“his style of painting was a reaction against cubism”