reduction

American  

[ri-duhk-shuhn] / rɪˈdʌk ʃən /

noun

1. the act of reducing or the state of being reduced.

2. the amount by which something is reduced or diminished.

3. a form produced by reducing a copy on a smaller scale.

4. Cell Biology. meiosis, especially the first meiotic cell division in which the chromosome number is reduced by half.

5. Chemistry. the process or result of reducing.

6. Movies. the process of making a print of a narrower gauge from a print of a wider gauge.

   the reduction of 35-millimeter films to 16-millimeter films for the school market.

7. a village or settlement of Indians in South America established and governed by Spanish Jesuit missionaries.

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reduction British  

/ rɪˈdʌkʃən /

noun

1. the act or process or an instance of reducing

2. the state or condition of being reduced

3. the amount by which something is reduced

4. a form of an original resulting from a reducing process, such as a copy on a smaller scale

5. a simplified form, such as an orchestral score arranged for piano

6. maths

   1. the process of converting a fraction into its decimal form

   2. the process of dividing out the common factors in the numerator and denominator of a fraction; cancellation

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reduction Scientific  

/ rĭ-dŭk′shən /

1. The changing of a fraction into a simpler form, especially by dividing the numerator and denominator by a common factor. For example, the fraction 8/12 can be reduced to 4/6, which can be further reduced to 2/3, in each case by dividing both the numerator and denominator by 2.

2. A chemical reaction in which an atom or ion gains electrons, thus undergoing a decrease in valence. If an iron atom having a valence of +3 gains an electron, the valence decreases to +2.

3. Compare oxidation

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reduction Cultural  

1. Any chemical reaction in which the atoms in a material take on electrons.

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Usage

Beginning students of chemistry are understandably puzzled by the term reduction: shouldn't a reduced atom or ion be one that loses electrons rather than gains them? The reason for the apparent contradiction comes from the early days of chemistry, where reduction and its counterpart, oxidation, were terms invented to describe reactions in which one substance lost an oxygen atom and the other substance gained it. In a reaction such as that between two molecules of hydrogen (2H₂) and one of oxygen (O₂) combining to produce two molecules of water (2H₂O), the hydrogen atoms have gained oxygen atoms and were said to have become “oxidized,” while the oxygen atoms have (as it were) lost them by attaching themselves to the hydrogens, and were said to have become “reduced.” Importantly, though, in the process of gaining an oxygen atom, the hydrogen atoms have had to give up their electrons and share them with the oxygen atoms, while the oxygen atoms have gained electrons. Thus comes the apparent paradox that the “reduced” oxygen has in fact gained something, namely electrons. Today the terms oxidation and reduction are used of any reaction, not just one involving oxygen, where electrons are (respectively) lost or gained.

Discover More

Reduction is the opposite of oxidation.

Other Word Forms

• antireduction
  adjective
• nonreduction
  noun
• nonreductional
  adjective
• overreduction
  noun
• proreduction
  adjective
• reductional
  adjective
• reductive
  adjective
• self-reduction
  noun

Etymology

Origin of reduction

First recorded in 1475–85; earlier reduccion, from Middle French reduction, from Latin reductiōn- (stem of reductiō ) “a bringing back,” equivalent to reduct(us) (past participle of redūcere “to lead back” ) + -iōn- noun suffix; see reduce, -ion

Explanation

Reduction is the act of cutting back or making smaller, like the reduction of a school budget that makes it necessary to eliminate art and music programs. The process of reducing something is reduction, or making it smaller. You can talk about a reduction of sugar in someone's diet or a reduction of prices at your favorite shoe store. In math, reduction means bringing fractions to their lowest common denominators. And, in cooking, a reduction is a thick sauce that's made by boiling away most of the liquid, or reducing it to its concentrated essence.

Example Sentences

Stevens told BBC Radio Wales Drive this would help anyone driving as part of their work and the VAT reduction from 20% to 5% for visitor attractions would help Welsh families in the summer holidays.

From BBC • May 21, 2026

“It was impressive to see that every dose of retatrutide resulted in clinically meaningful weight reduction for nearly all participants,” said lead investigator Ania Jastreboff, a professor at the Yale School of Medicine.

From Barron's • May 21, 2026

According to Ania Jastreboff, a Yale School of Medicine professor and lead investigator for the trial, every dose of retatrutide assessed resulted in clinically meaningful weight reduction for nearly all participants.

From The Wall Street Journal • May 21, 2026

Yet the region hasn’t seen a coinciding reduction in the amount of area burned by wildfires or the rate at which people are exposed to fire danger, he said.

From Los Angeles Times • May 20, 2026

Despite a good deal of opinion to the contrary, an item whose price has been increased by 50 percent and then reduced by 50 percent has had a net reduction in price of 25 percent.

From "Innumeracy: Mathematical Illiteracy and Its Consequences" by John Allen Paulos

Related Words

• contraction
• cut
• cutback
• devaluation
• discount
• rebate