<p><strong>Noun</strong></p><ul><li>a reverse movement or tendency; an action in a reverse direction or manner.</li><li>movement in the direction of political conservatism or extreme rightism.</li><li>action in response to some influence, event, etc.</li><li>action in response to a stimulus, as of the system or of a nerve, muscle, etc.</li><li>the action caused by the resistance to another action.</li><li>a return to the opposite physical condition, as after shock, exhaustion, or chill.</li><li>the specific cellular response to foreign matter, as in testing for allergies.</li><li>the reciprocal action of chemical agents upon each other; chemical change.</li><li>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.</li><li>the 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.</li><li>a decline in the market after an advance in prices.</li></ul>