[ ri-duhk-shuhn ]
/ rɪˈdʌk ʃən /
Save This Word!

Smoothly step over to these common grammar mistakes that trip many people up. Good luck!
Question 1 of 7
Fill in the blank: I can’t figure out _____ gave me this gift.

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


Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use reduction in a sentence

British Dictionary definitions for reduction

/ (rɪˈdʌkʃən) /

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 of reduction

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

Scientific definitions for reduction

[ rĭ-dŭkshən ]

The changing of a fraction into a simpler form, especially by dividing the numerator and denominator by a common factor. For example, the fraction 812 can be reduced to 46, which can be further reduced to 23, in each case by dividing both the numerator and denominator by 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.


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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for reduction


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

notes for reduction

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