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

Completed with a touch of lactose for a creamy finish, this hard seltzer is inspired by a classic summer frozen treat. — Jess Fleming, Twin Cities, 21 July 2026

The company produces a range of lactose-free products — which beyond milk, includes protein shakes. — Wyatte Grantham-Philips, Chicago Tribune, 17 July 2026

What allows many people to digest dairy products is a chainlike enzyme called lactase, which is produced in the small intestine and fits together like a puzzle piece with the complex sugar in milk called lactose. — Quanta Magazine, 15 July 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

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