noun \ˈlak-ˌtōs, -ˌtōz\

Definition of LACTOSE

: 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

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