reaction
re·ac·tion / rēˈakshən/ • n. an action performed or a feeling experienced in response to a situation or event: Carrie's immediate reaction was one of relief. ∎ (reactions) a person's ability to respond physically and mentally to external stimuli: a skilled driver with quick reactions. ∎ an adverse physiological response to a substance that has been breathed in, ingested, or touched: such allergic reactions as hay fever and asthma. ∎ a chemical process in which two or more substances act mutually on each other and are changed into different substances, or one substance changes into two or more other substances. ∎ Physics an analogous transformation of atomic nuclei or other particles. ∎ a mode of thinking or behaving that is deliberately different from previous modes of thought and behavior: the work of these painters was a reaction against fauvism. ∎ opposition to political or social progress or reform: the institution is under threat from the forces of reaction. ∎ Physics repulsion or resistance exerted in opposition to the impact or pressure of another body; a force equal and opposite to the force giving rise to it.DERIVATIVES: re·ac·tion·ist / -nist/ n. & adj.