lactose

noun

lac·​tose ˈlak-ˌtōs 

-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

To possibly benefit from lower blood sugar, consider choosing whole milk, which has more fat and lactose than skim milk. — Cristina Mutchler, Verywell Health, 23 June 2026

Other supplements come in gelatin capsules, made from collagen derived from cow and pig bones and hides, or mixed with dairy binders such as lactose and sodium caseinate. — Burkhard Bilger, New Yorker, 29 June 2026

Kefir Often Has Less Lactose Milk contains a high amount of lactose. — Merve Ceylan, Health, 15 May 2026

These bacteria ferment milk sugar, or lactose, into flavor compounds and organic acids, which give the butter a mild tang and complex flavor. — Rosemary Trout, The Conversation, 10 June 2026

Word History

Etymology

International Scientific Vocabulary

First Known Use

1847, in the meaning defined above

Phrases Containing lactose

• lactose intolerant

Rhymes for lactose

• galactose

Kids Definition

lactose

noun

lac·​tose ˈlak-ˌtōs 

: 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 

: 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