reaction

/riˈækʃən/

/riˈækʃən/

Other forms: reactions

A reaction is an action taken in response to something. If you're telling your parents that you want to move out, you'll see by their reaction that they're sad about it.

A reaction is often a physical in nature. A chemical reaction describes the way a chemical behaves when combined with another substance. The way your body responds to a medication or external influence is a physical reaction. Think of the way cold air causes you to get goose bumps on your arms. It can also describe something more emotional, for instance a person’s reaction of laughter when told a funny story.

Definitions of reaction

1. noun

   an idea evoked by some experience
   “his reaction to the news was to start planning what to do”

   type of:

   idea, thought

   the content of cognition; the main thing you are thinking about
2. noun

   a response that reveals a person's feelings or attitude
   “he was pleased by the audience's reaction to his performance”

   “John feared his mother's reaction when she saw the broken lamp”

   type of:

   response

   a result
3. noun

   doing something in opposition to another way of doing it that you don't like
   “his style of painting was a reaction against cubism”

   types:

   backlash

   an adverse reaction to some political or social occurrence

   white backlash, whitelash

   backlash by white racists against black civil rights advances

   type of:

   opposition, resistance

   the action of opposing something that you disapprove or disagree with
4. noun

   extreme conservatism in political or social matters
   “the forces of reaction carried the election”

   type of:

   conservatism, conservativism

   a political or theological orientation advocating the preservation of the best in society and opposing radical changes
5. noun

   a bodily process occurring due to the effect of some antecedent stimulus or agent
   “a bad reaction to the medicine”

   synonyms: response

   types:

   automatism

   any reaction that occurs automatically without conscious thought or reflection (especially the undirected behavior seen in psychomotor epilepsy)

   rebound

   a reaction to a crisis or setback or frustration

   overreaction

   an excessive reaction; a reaction with inappropriate emotional behavior

   Fere phenomenon, GSR, Tarchanoff phenomenon, electrical skin response, electrodermal response, galvanic skin response, psychogalvanic response

   a change in the electrical properties of the skin in response to stress or anxiety; can be measured either by recording the electrical resistance of the skin or by recording weak currents generated by the body

   immune reaction, immune response, immunologic response

   a bodily defense reaction that recognizes an invading substance (an antigen: such as a virus or fungus or bacteria or transplanted organ) and produces antibodies specific against that antigen

   tropism

   an involuntary orienting response; positive or negative reaction to a stimulus source

   taxis

   a locomotor response toward or away from an external stimulus by a motile (and usually simple) organism

   kinesis

   a movement that is a response to a stimulus but is not oriented with respect to the source of stimulation

   double take

   a delayed reaction indicating surprise

   inborn reflex, innate reflex, instinctive reflex, physiological reaction, reflex, reflex action, reflex response, unconditioned reflex

   an automatic instinctive unlearned reaction to a stimulus

   learned reaction, learned response

   a reaction that has been acquired by learning

   passage, passing

   a bodily reaction of changing from one place or stage to another

   answer

   a nonverbal reaction

   transfusion reaction

   reaction of the body to a transfusion of blood that is not compatible with its own blood; an adverse reaction can range from fever and hives to renal failure and shock and death

   accommodation reflex

   reflex changes in the eyes that enable an object to be focused on the retina

   Babinski, Babinski reflex, Babinski sign

   extension upward of the toes when the sole of the foot is stroked firmly on the outer side from the heel to the front; normal in infants under the age of two years but a sign of brain or spinal cord injury in older persons

   belch, belching, burp, burping, eructation

   a reflex that expels gas noisily from the stomach through the mouth

   blink, blinking, eye blink, nictation, nictitation, wink, winking

   a reflex that closes and opens the eyes rapidly

   blush, flush

   sudden reddening of the face (as from embarrassment or guilt or shame or modesty)

   disgorgement, emesis, regurgitation, vomit, vomiting

   the reflex act of ejecting the contents of the stomach through the mouth

   defecation reflex, rectal reflex

   normal response to the presence of feces in the rectum

   oscitance, oscitancy, yawn, yawning

   an involuntary intake of breath through a wide open mouth; usually triggered by fatigue or boredom

   electric shock, electrical shock, shock

   a reflex response to the passage of electric current through the body

   gulp, gulping

   a spasmodic reflex of the throat made as if in swallowing

   anamnestic reaction, anamnestic response

   renewed rapid production of an antibody on the second (or subsequent) encounter with the same antigen

   humoral immune response

   an immune response (chiefly against bacterial invasion) that is mediated by B cells

   cell-mediated immune response

   an immune response (chiefly against viral or fungal invasions or transplanted tissue) that involves T cells

   complement fixation

   an immune response in which an antigen-antibody combination inactivates a complement (so it is unavailable to participate in a second antigen-antibody combination)

   ergotropism

   an affinity for work

   geotropism

   an orienting response to gravity

   heliotropism

   an orienting response to the sun

   meteortropism

   an effect of climate on biological processes (as the effect on joint pains etc.)

   neurotropism

   an affinity for neural tissues

   phototropism

   an orienting response to light

   trophotropism

   an orienting response to food

   thermotropism

   an orienting response to warmth

   chemotaxis

   movement by a cell or organism in reaction to a chemical stimulus

   acquired reflex, conditional reaction, conditional reflex, conditional response, conditioned reaction, conditioned reflex, conditioned response

   an acquired response that is under the control of (conditional on the occurrence of) a stimulus

   knee jerk, knee-jerk reflex, patellar reflex

   a reflex extension of the leg resulting from a sharp tap on the patellar tendon

   light reflex, miosis, myosis, pupillary reflex

   reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller

   mydriasis

   reflex pupillary dilation as a muscle pulls the iris outward; occurs in response to a decrease in light or certain drugs

   micturition reflex

   relaxation of the urethral sphincter in response to increased pressure in the bladder

   gag reflex, pharyngeal reflex

   normal reflex consisting of retching; may be produced by touching the soft palate in the back of the mouth

   goose bump, goose pimple, goose skin, goosebump, gooseflesh, horripilation, pilomotor reflex

   reflex erection of hairs of the skin in response to cold or emotional stress or skin irritation

   plantar reflex

   flexion of the toes when the sole of the foot is stroked firmly on the outer side from the heel to the front in persons over the age of 2 years; under 2 years the results should be extension of the toes (Babinski reflex)

   rooting reflex

   reflex consisting of head-turning and sucking movements elicited in a normal infant by gently stroking the side of the mouth or cheek

   jump, start, startle

   a sudden involuntary movement

   myotactic reflex, stretch reflex

   reflex contraction of a muscle when an attached tendon is pulled; important in maintaining erect posture

   suckling reflex

   reflex behavior in newborn mammals; includes finding and grasping the nipple in the mouth and sucking on it and swallowing the milk

   shake, shiver, tremble

   a reflex motion caused by cold or fear or excitement

   sneeze, sneezing, sternutation

   a symptom consisting of the involuntary expulsion of air from the nose

   hiccough, hiccup, singultus

   (usually plural) the state of having reflex spasms of the diaphragm accompanied by a rapid closure of the glottis producing an audible sound; sometimes a symptom of indigestion

   type of:

   activity, bodily function, bodily process, body process

   an organic process that takes place in the body
6. noun

   (mechanics) the equal and opposite force that is produced when any force is applied to a body
   “every action has an equal and opposite reaction”

   type of:

   force

   (physics) the influence that produces a change in a physical quantity
7. noun

   (chemistry) a process in which one or more substances are changed into others
   synonyms: chemical reaction

   types:

   addition reaction

   a chemical reaction in which one molecule is added to another

   aldol reaction

   a reaction of aldehydes resulting in an aldol

   chain reaction

   a series of chemical reactions in which the product of one is a reactant in the next

   chemical equilibrium, equilibrium

   a chemical reaction and its reverse proceed at equal rates

   chemical decomposition reaction, decomposition, decomposition reaction

   (chemistry) separation of a substance into two or more substances that may differ from each other and from the original substance

   displacement, displacement reaction

   (chemistry) a reaction in which an elementary substance displaces and sets free a constituent element from a compound

   double decomposition, double decomposition reaction, metathesis

   a chemical reaction between two compounds in which parts of each are interchanged to form two new compounds (AB+CD=AD+CB)

   elimination reaction

   a chemical reaction in which a molecule decomposes to two different molecules

   endothermic reaction

   a chemical reaction accompanied by the absorption of heat

   exothermic reaction

   a chemical reaction accompanied by the evolution of heat

   hydrolysis

   a chemical reaction in which water reacts with a compound to produce other compounds; involves the splitting of a bond and the addition of the hydrogen cation and the hydroxide anion from the water

   neutralisation, neutralisation reaction, neutralization, neutralization reaction

   a chemical reaction in which an acid and a base interact with the formation of a salt; with strong acids and bases the essential reaction is the combination of hydrogen ions with hydroxyl ions to form water

   oxidation, oxidisation, oxidization

   the process of oxidizing; the addition of oxygen to a compound with a loss of electrons; always occurs accompanied by reduction

   oxidation-reduction, oxidoreduction, redox

   a reversible chemical reaction in which one reaction is an oxidation and the reverse is a reduction

   photochemical reaction

   a chemical reaction produced by the action of light

   reducing, reduction

   any process in which electrons are added to an atom or ion (as by removing oxygen or adding hydrogen); always occurs accompanied by oxidation of the reducing agent

   saponification

   a chemical reaction in which an ester is heated with an alkali (especially the alkaline hydrolysis of a fat or oil to make soap)

   acid-base balance, acid-base equilibrium

   (physiology) the normal equilibrium between acids and alkalis in the body

   calcination

   the conversion of metals into their oxides as a result of heating to a high temperature

   burning, combustion

   a process in which a substance reacts with oxygen to give heat and light

   double replacement reaction

   a chemical reaction between two compounds where the positive ion of one compound is exchanged with the positive ion of another compound

   electrolysis

   (chemistry) a chemical decomposition reaction produced by passing an electric current through a solution containing ions

   light reaction

   the first stage of photosynthesis during which energy from light is used for the production of ATP

   nitrification

   the oxidation of ammonium compounds in dead organic material into nitrates and nitrites by soil bacteria (making nitrogen available to plants)

   rust, rusting

   the formation of reddish-brown ferric oxides on iron by low-temperature oxidation in the presence of water

   type of:

   chemical action, chemical change, chemical process

   (chemistry) any process determined by the atomic and molecular composition and structure of the substances involved