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

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

Filtration separates milk protein from water, lactose, and minerals, resulting in thicker, more concentrated milk with higher protein and less liquid. — Amy Brownstein, Verywell Health, 12 Aug. 2026

Paola said her grandson, who had been drinking only lactose-free milk, has been given whole milk at Dilley. — Laura Romero, ABC News, 6 Aug. 2026

Made with the same fresh milk and real cream, Philadelphia guarantees its lactose-free recipe delivers the same rich flavor as its original cream cheese. — Claire Hoppe Norgaard, Better Homes & Gardens, 30 July 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