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See more synonyms for lactose on Thesaurus.com
  1. Biochemistry. a disaccharide, C12H22O11, present in milk, that upon hydrolysis yields glucose and galactose.
  2. a white, crystalline, sweet, water-soluble commercial form of this compound, obtained from whey and used in infant feedings, in confections and other foods, in bacteriological media, and in pharmacology as a diluent and excipient.
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Origin of lactose

First recorded in 1855–60; lact- + -ose2
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words


Examples from the Web for lactose

Historical Examples

  • Control of casein or lactose, on the contrary, is not nearly so practicable.

    The Book of Cheese

    Charles Thom and Walter Warner Fisk

  • Levulose, lactose, and some others are occasionally met with.

  • These are all characteristic reactions of lactose or milk sugar.

  • Lactose exists in milk and has the same formula as cane-sugar.

    Encyclopedia of Diet

    Eugene Christian

  • The lactose is converted into lactic acid by means of a special ferment.

    A Practical Physiology

    Albert F. Blaisdell

British Dictionary definitions for lactose


  1. a white crystalline disaccharide occurring in milk and used in the manufacture of pharmaceuticals and baby foods. Formula: C 12 H 22 O 11Also called: milk sugar
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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

Word Origin and History for lactose


sugar from milk, 1858, from French, coined by French chemist Marcelin-Pierre-Eugène Berthelot (1827-1907) from Latin lac (genitive lactis) "milk" (see lactation) + chemical suffix -ose (2).

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Online Etymology Dictionary, © 2010 Douglas Harper

lactose in Medicine


  1. A disaccharide in milk that hydrolyzes to yield glucose and galactose.milk sugar
  2. A white crystalline substance obtained from whey and used in infant foods and in pharmaceuticals as a diluent and excipient.milk sugar
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

lactose in Science


  1. A white crystalline disaccharide consisting of a glucose and a galactose molecule, found in milk and used in the manufacture of various other foods. Chemical formula: C12H22O11.
  2. The inability to digest lactose properly is called lactose intolerance. It is caused by a deficiency of the enzyme lactase and marked by abdominal cramping and other symptoms after ingesting lactose.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.