Meaning of REACTION in English

rē+ noun

( -s )

Etymology: New Latin reaction-, reactio, from reactus (past participle of reagere to react) + Latin -ion-, -io -ion — more at react


a. : exertion of reciprocal or counteracting force or influence

the reaction between an individual and his environment

b. : action in opposition to some force or influence

reaction against dictatorship

c. : movement in or tendency toward a reverse direction : return to a prior condition

a strong reaction in stock prices

d. : a tendency toward or movement in support of a former especially outmoded or repressive political or social condition, policy, or form of government

mixture of sober conservatism, timid standpattism, and angry reaction — Clinton Rossiter


a. : a particular response to a particular treatment, situation, or other stimulus

watched her reaction to the news

b. : bodily response to or activity aroused by a stimulus:

(1) : motor response (as muscular movement or secretion) to stimulation

(2) : the whole sensorimotor process comprising intellectual and emotional elements as well as pure motor response : total response of an organism to a stimulus


(1) : an action induced by vital resistance to some other action

inflammatory reaction to bacterial infection

especially : the specific result (as hemolysis, local inflammation, or a rise in bodily temperature) characteristically evoked in cells or tissues or in vitro by a foreign substance and used in various serological tests to determine specific sensitivities or the presence of particular infection

the tuberculin reaction

the precipitin reaction

allergic reactions

(2) : depression or exhaustion of vital force consequent on overexertion or overstimulation

(3) : heightened activity and overaction succeeding depression or shock

(4) : a psychosis, psychoneurosis, or other mental or emotional disorder forming an individual's response to his life situation

an anxiety reaction

a schizophrenic reaction

3. : the force that a body subjected to the action of a force from another body exerts in the opposite direction



(1) : chemical transformation or change : the reversible or irreversible interaction of molecules, atoms, ions, or radicals to form one or more new substances

the reaction of acid with base

the reaction of hydrogen with oxygen gives water

endothermic and exothermic reactions

— see equation 2b, order of a reaction ; compare catalysis , decomposition , polymerization , substitution , synthesis

(2) : the state resulting from such a reaction

an alkaline reaction

b. : a process involving change in atomic nuclei (as the disintegration of uranium 239 into neptunium and an electron or the union of heavy-hydrogen nuclei to form helium nuclei) — called also nuclear reaction ; compare chain reaction , fission , fusion , spallation

5. : the effect of organisms upon their habitat — compare coaction

6. : the degree of acidity or alkalinity of soil

Webster's New International English Dictionary.      Новый международный словарь английского языка Webster.