[ lak-tohs ]
See synonyms for lactose on
  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.

Origin of lactose

First recorded in 1855–60; lact- + -ose2

Words Nearby lactose Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

How to use lactose in a sentence

  • Besides being an important part of milk itself, lactose is a valuable by-product in the manufacture of cheese.

    Woman's Institute Library of Cookery, Vol. 2 | Woman's Institute of Domestic Arts and Sciences
  • Members of this group uniformly ferment the lactose with the production of the gases, carbon dioxide and hydrogen.

    The Book of Cheese | Charles Thom and Walter Warner Fisk
  • It seems that the tendency is toward an increase of lactic acid in the cheese long after the lactose has disappeared.

    The Book of Cheese | Charles Thom and Walter Warner Fisk
  • However, these acids were found in increasing amounts during the ripening process and after the lactose had disappeared.

    The Book of Cheese | Charles Thom and Walter Warner Fisk
  • Weigh out: lactose 10 grammes and dissolve in the fluid agar.

British Dictionary definitions for lactose


/ (ˈlæktəʊs, -təʊz) /

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

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 lactose


[ lăktōs′ ]

  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.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.