The Collaborative International Dictionary of English v.0.48:

Galactose \Ga*lac"tose\, n. (Chem.)
   A white, crystalline sugar, C6H12O6, isomeric with
   dextrose, obtained by the decomposition of milk sugar, and
   also from certain gums. When oxidized it forms mucic acid.
   Called also lactose (though it is not lactose proper).
   [1913 Webster]

WordNet (r) 3.0 (2006):

galactose
    n 1: a simple sugar found in lactose [syn: galactose, brain
         sugar]