Medical Dictionary


noun re·ac·tion \rē-ˈak-shən\

Medical Definition of REACTION

:  the act or process or an instance of reacting
:  bodily response to or activity aroused by a stimulus: a :  an action induced by vital resistance to another action; especially :  the response of tissues to a foreign substance (as an antigen or infective agent) b :  depression or exhaustion due to excessive exertion or stimulation c :  abnormally heightened activity succeeding depression or shock d :  a mental or emotional disorder forming an individual's response to his or her life situation
:  the force that a body subjected to the action of a force from another body exerts in the opposite direction
a (1) :  chemical transformation or change :  the interaction of chemical entities (2) :  the state resulting from such a reaction b :  a process involving change in atomic nuclei
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