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

As Shapiro explains, lactose-free dairy milk technically has the same electrolyte and protein profile as regular milk; the only difference is that the lactose is just broken down into simpler sugars. — Veronica Cristino, Vogue, 29 Sep. 2026

Natural sugars include lactose in dairy products or fructose in fruits and fruit products. — Jennifer Lefton, Verywell Health, 21 Sep. 2026

Because of this, Halperin says many people with mild lactose intolerance tolerate kefir better than ordinary milk, though kefir is not lactose-free unless labeled accordingly. — Daryl Austin, USA Today, 16 Sep. 2026

As part of the strategy to widen cream cheese’s appeal to shoppers, Philadelphia also launched a lactose-free version earlier this year. — Amelia Lucas, CNBC, 15 Sep. 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