Source : Webster's Revised Unabridged Dictionary (1913)

Lactose \Lac"tose`\, n.
   1. (Physiol. Chem.) 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
      {lactin}.

   2. (Chem.) See {Galactose}.

Source : WordNet®

lactose
     n : a sugar comprising one glucose molecule linked to a
         galactose molecule; occurs only in milk; "cow's milk
         contains about 4.7% lactose" [syn: {milk sugar}]