lactose

noun

1. a sugar comprising one glucose molecule linked to a galactose molecule; occurs only in milk

   noun.substance

   Examples

   Cow's milk contains about 4.7% lactose.

   Synonyms milk sugar

   Source: WordNet 3.0

2. Sugar of milk or milk sugar; a crystalline sugar present in milk, and separable from the whey by evaporation and crystallization. It has a slightly sweet taste, is dextrorotary, and is much less soluble in water than either cane sugar or glucose. Formerly called <i>lactin</i>.

   noun

   Source: webster1913