The Collaborative International Dictionary of English v.0.48:

Carbohydrate \Car`bo*hy"drate\, n. [Carbon + hydrate.] (Physiol.
   Chem.)
   One of a group of compounds including the sugars, starches,
   and gums, which contain six (or some multiple of six) carbon
   atoms, united with a variable number of hydrogen and oxygen
   atoms, but with the two latter always in proportion as to
   form water; as dextrose, C6H12O6.
   [1913 Webster]

WordNet (r) 3.0 (2006):

carbohydrate
    n 1: an essential structural component of living cells and
         source of energy for animals; includes simple sugars with
         small molecules as well as macromolecular substances; are
         classified according to the number of monosaccharide groups
         they contain [syn: carbohydrate, saccharide, sugar]