Re-ăc'tion, n.

noun

n. [Prefix re and action; Fr. réaction, Sp. reaccion, It. reazione.]

Any action in resisting other action or power; counter tendency; movement in a contrary direction; reverse action.
(Chem.) The mutual or reciprocal action of chemical agents upon each other; the manifestation of distinctive characters.
(Med.) An action or its manifestation induced by vital resistance to some other action; depression or exhaustion of vital force consequent on over-exertion, or over-stimulation.
(Mech.) The force which a body subjected to the action of a force from another body exerts upon that body in the opposite direction.
(Politics.) Backward tendency from revolution, reform, or progress.

The new king had, at the very moment at which his fame and fortune reached the highest point, predicted the coming reaction. Macaulay.