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1. The act or process of reducing.
2. The result of reducing: a reduction in absenteeism.
3. The amount by which something is lessened or diminished: a reduction of 12 percent in violent crime.
4. A sauce that has been thickened or concentrated by boiling.
5. Biology The first meiotic division, in which the chromosome number is reduced from diploid to haploid. Also called reduction division.
6. Chemistry
a. A decrease in positive valence or an increase in negative valence by the gaining of electrons.
b. A reaction in which hydrogen is combined with a compound.
c. A reaction in which oxygen is removed from a compound.
7. Mathematics
a. The canceling of common factors in the numerator and denominator of a fraction.
b. The converting of a fraction to its decimal equivalent.
c. The converting of an expression or equation to its simplest form.

[Middle English reduccioun, restoration, action of bringing back to a former state, from Middle French reduction, from Old French redution, from Latin reductiō, reductiōn-, from reductus, past participle of redūcere, to bring back; see reduce.]

re·duc′tion·al adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


1. of, characterized by, or relating to reduction
2. (Mathematics) of, characterized by, or relating to reduction
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
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References in periodicals archive ?
b reductional: perodicka sustavaprvkov -periodicka sustava 'periodic table'
This reductional stage is compared to the previous one in the following scheme (innovations are in bold):
Low chromosome number and post reductional X0 in Gelus californicus (Lec.) (Coleoptera: Curculionidae).
Firstly, Luzula was shown to have a special type of meiosis, in which the first division is equatorial and the second reductional. This phenomenon has been studied in Luzula elegans by Malheiros and Garde (1947).
Although the potential impact of the expression of meiotic proteins during mitosis in causing CIN has been suggested [17-21] and a role in reductional division in irradiated polyploid cells has been noted [22], thus far there has been no research directly evaluating the potential direct role of meiosis proteins in the creation of CIN.
Due to the marine habits of its constituent species, their uniformly wingless morphology, and other reductional character states, the taxonomic status of Hermatobates has been unsettled for over 100 years.
In telophase I, ten autosomes move towards each pole after reductional division while the X chromosome lags behind, but finally reach one of the poles (Fig.