lactose

noun

lac·​tose ˈlak-ˌtōs How to pronounce lactose (audio)
-ˌtōz
: a disaccharide sugar C12H22O11 that is present in milk and yields glucose and galactose upon hydrolysis and yields especially lactic acid upon fermentation

Examples of lactose in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Turning a lactose-digestion difference into a deficiency has done more to reinforce narratives of racial hierarchy than to improve public health. — Hilary Smith, The Conversation, 25 Aug. 2026 For me, that means a calorie-conscious, gluten- and lactose-free plan with hyper-specific protein targets. — Abby Montanez, Robb Report, 23 Aug. 2026 As for their frosting, the main ingredient is lactose-free milk, along with a few secret ingredients. — Maddie Rhodes, USA Today, 21 Aug. 2026 Thus, feta is considered easier to digest than most other cheeses, even for those with a slight lactose intolerance. — Alessandra Signorelli, Vogue, 14 Aug. 2026 See All Example Sentences for lactose

Word History

Etymology

International Scientific Vocabulary

First Known Use

1847, in the meaning defined above

Time Traveler
The first known use of lactose was in 1847

Phrases Containing lactose

Rhymes for lactose

See All Rhymes for lactose

Browse Nearby Words

lactoprene
lactose
lactose intolerant
See all Nearby Words

Cite this Entry

“Lactose.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/lactose. Accessed 1 Sep. 2026.

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Kids Definition

lactose

noun
lac·​tose ˈlak-ˌtōs How to pronounce lactose (audio)
: a sugar present in milk that breaks down to give glucose and galactose and on fermentation gives especially lactic acid

called also milk sugar

Medical Definition

lactose

noun
lac·​tose ˈlak-ˌtōs, -ˌtōz How to pronounce lactose (audio)
: a disaccharide sugar C12H22O11 that is present in milk, yields glucose and galactose upon hydrolysis, yields especially lactic acid upon fermentation, and is used chiefly in foods, medicines, and culture media (as for the manufacture of penicillin)

called also milk sugar

More from Merriam-Webster on lactose

Britannica.com: Encyclopedia article about lactose

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