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

All menus, including those for kids, are clearly labeled with designations such as vegan, gluten-free, lactose-free, contains nuts, sustainably sourced, and locally sourced. —Kathryn Romeyn, Travel + Leisure, 28 Sep. 2025

Whey has all essential amino acids but contains lactose. —Merve Ceylan, Health, 28 Sep. 2025

Dairy Products Dairy products like milk and cheese contain lactose, a sugar that is not always easily broken down in the digestive tract. —Cristina Mutchler, Verywell Health, 24 Sep. 2025

Other foods that aren’t necessarily toxic, but can still cause health problems, include dairy products, which may lead to digestive issues because many dogs lack the enzyme to break down lactose. —Maria Azzurra Volpe, MSNBC Newsweek, 23 Sep. 2025

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