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WordReference Random House Learner's Dictionary of American English © 2024re•ac•tion /riˈækʃən/USA pronunciation n. - an action in a reverse direction or manner:[countable]For every action there is an equal and opposite reaction.
- Government[uncountable] a tendency to return to an earlier political system or social order.
- action in response to some influence, event, etc.: [uncountable]the nation's reaction to the president's speech.[countable]My reactions are mixed.
- Medicine[countable]
- Medicinea response by the body to an action or condition.
- a change in the body that shows sensitivity to foreign matter:an allergic reaction to cat hair.
- Chemistry[countable] the action of chemical agents upon each other.
WordReference Random House Unabridged Dictionary of American English © 2024re•ac•tion (rē ak′shən),USA pronunciation n. - a reverse movement or tendency;
an action in a reverse direction or manner. - Governmentmovement in the direction of political conservatism or extreme rightism.
- action in response to some influence, event, etc.:the nation's reaction to the President's speech.
- Physiologyaction in response to a stimulus, as of the system or of a nerve, muscle, etc.
- Medicine
- Medicinethe action caused by the resistance to another action.
- Medicinea return to the opposite physical condition, as after shock, exhaustion, or chill.
- Microbiology, Immunology[Bacteriol., Immunol.]the specific cellular response to foreign matter, as in testing for allergies.
- Chemistrythe reciprocal action of chemical agents upon each other;
chemical change. - PhysicsAlso called nuclear reaction. a process in which a nucleus that is bombarded by a photon, particle, or other nucleus, emits a nucleon, alpha particle, or the like, without a significant change in its atomic weight.
- Mechanicsthe instantaneous response of a system to an applied force, manifested as the exertion of a force equal in magnitude but opposite in direction to the applied force.
- Business[Com.]a decline in the market after an advance in prices.
- re- + action, modeled on react 1635–45
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