Reaction

n. action made in response to a stimulus; return to a previous state, restoration of a past condition

A reaction is usually any response caused by some other event:Adverse drug reactionChemical reactionLight reactionNuclear reactionReaction (physics), as defined by Newton's third lawReflex reactionReactionary, a political tendencyThe word Reaction may also refer to:Reaction Records, a record labelReAction, an AmigaOS GUI
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Noun
1. a 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"
(hypernym) response
(derivation) react, respond
2. a bodily process occurring due to the effect of some foregoing stimulus or agent; "a bad reaction to the medicine"; "his responses have slowed with age"
(synonym) response
(hypernym) bodily process, body process, bodily function, activity
(hyponym) automatism
(derivation) react, respond
3. (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"
(synonym) chemical reaction
(hypernym) chemical process, chemical change, chemical action
(hyponym) addition reaction
(derivation) react
(classification) chemistry, chemical science
4. an idea evoked by some experience; "his reaction to the news was to start planning what to do"
(hypernym) idea, thought
5. doing something in opposition to another way of doing it that you don't like; "his style of painting was a reaction against cubism"
(hypernym) resistance, opposition
(hyponym) backlash
6. extreme conservatism in political or social matters; "the forces of reaction carried the election"
(hypernym) conservatism, conservativism
7. (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"
(hypernym) force
(classification) mechanics

n. reaction, response, feedback

(n.)
The mutual or reciprocal action of chemical agents upon each other, or the action upon such chemical agents of some form of energy, as heat, light, or electricity, resulting in a chemical change in one or more of these agents, with the production of new compounds or the manifestation of distinctive characters. See Blowpipe reaction, Flame reaction, under Blowpipe, and Flame.
  

(n.)
The force which a body subjected to the action of a force from another body exerts upon the latter body in the opposite direction.
  

(n.)
Backward tendency or movement after revolution, reform, or great progress in any direction.
  

(n.)
Any action in resisting other action or force; counter tendency; movement in a contrary direction; reverse action.
  

(n.)
An action induced by vital resistance to some other action; depression or exhaustion of vital force consequent on overexertion or overstimulation; heightened activity and overaction succeeding depression or shock.