reaction

[ ree-ak-shuhn ]

noun

1. a reverse movement or tendency; an action in a reverse direction or manner.
2. movement in the direction of political conservatism or extreme rightism.
3. action in response to some influence, event, etc.:

   the nation's reaction to the president's speech.

4. Physiology. action in response to a stimulus, as of the system or of a nerve, muscle, etc.
5. Medicine/Medical.
   1. the action caused by the resistance to another action.
   2. a return to the opposite physical condition, as after shock, exhaustion, or chill.
6. Bacteriology, Immunology. the specific cellular response to foreign matter, as in testing for allergies.
7. Also called chemical reaction. Chemistry. the reciprocal action of chemical agents upon each other; chemical change.
8. Also called nuclear reaction. Physics. 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.
9. Mechanics. 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.
10. Commerce. a decline in the market after an advance in prices.

reaction

/ rɪˈækʃən /

noun

1. a response to some foregoing action or stimulus
2. the reciprocal action of two things acting together
3. opposition to change, esp political change, or a desire to return to a former condition or system
4. a response indicating a person's feelings or emotional attitude
5. med
   1. any effect produced by the action of a drug, esp an adverse effect Compare side effect
   2. any effect produced by a substance (allergen) to which a person is allergic
6. short for chemical reaction nuclear reaction
7. stock exchange a sharp fall in price interrupting a general rise

reaction

/ rē-ăk′shən /

1. A rearrangement of the atoms or molecules of two or more substances that come into contact with each other, resulting in the formation of one or more new substances. Chemical reactions are caused by electrons of one substance interacting with those of another. The reaction of an acid with a base, for example, results in the creation of a salt and water. Some, but not all, reactions can be reversed.
2. See nuclear reaction
3. An action that results directly from or counteracts another action, especially the change in a body's motion as a result of a force applied to it. Some reactions counteract forces and are not readily apparent. When an object rests on a surface, such as a table, for example, the downward force it applies to the surface is counteracted by an equal but upwards force, or reaction, applied by the surface.
4. See more at Newton's laws of motion
5. A response to a stimulus, such as a reflex.
6. The response of cells or tissues to an antigen, as in a test for immunization.

Usage

Reaction is used to refer both to an instant response ( her reaction was one of amazement ) and to a considered response in the form of a statement ( the Minister gave his reaction to the court's decision ). Some people think this second use is incorrect

Derived Forms

• reˈactional, adjective

Other Words From

• re·action·al adjective
• re·action·al·ly adverb
• anti·re·action adjective noun
• counter·re·action noun
• nonre·action noun
• super·re·action noun

Word History and Origins

Origin of reaction¹

First recorded in 1635–45; re- + action, modeled on react

Example Sentences

What was the reaction when Dr. Phil’s camp found out about your show?

From Los Angeles Times

"History will judge us based on our actions and reactions," read the caption.

From BBC

Participants experienced minor side effects from the treatment but none had serious adverse reactions.

From Science Daily

These high concentrations result in unique chemical reactions within cancer cells that render the cells more vulnerable to chemo- and radiation therapies.

From Science Daily

Ukraine’s public reaction was positive but muted, with President Volodymyr Zelensky saying any long-range missiles by Ukraine’s forces to take aim at Russia would “speak for themselves.”

From Los Angeles Times

Related Words

• answer
• attitude
• backlash
• feedback
• feeling
• opinion
• reception
• reply
• return