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

Due to the natural fermentation process, Greek yogurt is also a great option for people who are lactose-sensitive. —Philipp Wehsack, Vogue, 28 Mar. 2026

Diarrhea Limit foods and beverages that contain sugar alcohols, high-fructose corn syrup and lactose, which might make diarrhea worse. —CBS News, 27 Mar. 2026

Reach for lactose-free milk, says Manaker. —Kirsten Nunez, Martha Stewart, 15 Mar. 2026

Whey has all essential amino acids but contains lactose. —Merve Ceylan, Health, 26 Feb. 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