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[ri-duhk-shuh n] /rɪˈdʌk ʃən/
the act of reducing or the state of being reduced.
the amount by which something is reduced or diminished.
a form produced by reducing; a copy on a smaller scale.
Cell Biology. meiosis, especially the first meiotic cell division in which the chromosome number is reduced by half.
Chemistry. the process or result of reducing.
Movies. the process of making a print of a narrower gauge from a print of a wider gauge:
the reduction of 35-mm films to 16-mm for the school market.
a village or settlement of Indians in South America established and governed by Spanish Jesuit missionaries.
Origin of reduction
1475-85; earlier reduccion < Middle French reduction < Latin reductiōn- (stem of reductiō) a bringing back, equivalent to reduct(us) (past participle of redūcere; see reduce) + -iōn- -ion
Related forms
reductional, adjective
antireduction, adjective
nonreduction, noun
nonreductional, adjective
overreduction, noun
proreduction, adjective
self-reduction, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for reduction
Contemporary Examples
Historical Examples
  • Gotleib contended that Arledge could sustain the reduction required.

    The Spenders Harry Leon Wilson
  • As a rule, however, the associations will not hear of even such a reduction.

    Freeland Theodor Hertzka
  • The reduction in rent in this case was at least a third of the total.

    The Enclosures in England Harriett Bradley
  • His debts of 1000 had been paid, and his allowance of 300 threatened with the reduction of a third.

    James Boswell William Keith Leask
  • This chute, Fuller had said, led to the outside at the back of the reduction plant.

    Vulcan's Workshop Harl Vincent
British Dictionary definitions for reduction


the act or process or an instance of reducing
the state or condition of being reduced
the amount by which something is reduced
a form of an original resulting from a reducing process, such as a copy on a smaller scale
a simplified form, such as an orchestral score arranged for piano
  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
Derived Forms
reductive, adjective
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for reduction

early 15c., "a restoring to a former state; a subjugation" (of a people, etc.), from Middle French reducion (13c., Modern French réduction) and directly from Latin reductionem (nominative reductio) "a leading back, restoration," noun of action from past participle stem of reducere (see reduce). Meaning "diminution, a lessening" is from 1670s; chemical sense of "reversion to a simpler form" is from 1660s.

Online Etymology Dictionary, © 2010 Douglas Harper
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reduction in Medicine

reduction re·duc·tion (rĭ-dŭk'shən)

  1. The act, process, or result of reducing.

  2. The amount by which something is lessened or diminished.

  3. Restoration of an injured or dislocated part to its normal anatomical relation by surgery or manipulation. Also called repositioning.

  4. The first meiotic division, in which the chromosome number is reduced. Also called reduction division, reduction of chromosomes.

  5. A decrease in positive valence or an increase in negative valence by the gaining of electrons.

  6. A reaction in which hydrogen is combined with a compound.

  7. A reaction in which oxygen is removed from a compound.

re·duc'tion·al adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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reduction in Science
  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. Compare oxidation.

Our Living Language  : 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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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reduction in Culture

reduction definition

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

Note: Reduction is the opposite of oxidation.
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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