The Collaborative International Dictionary of English v.0.48:

Ketone \Ke"tone\ (k[=e]"t[=o]n), n. [Cf. Acetone.] (Chem.)
   One of a large class of organic substances resembling the
   aldehydes, obtained by the distillation of certain salts of
   organic acids and consisting of carbonyl (CO) united with
   two hydrocarbon radicals. In general the ketones are
   colorless volatile liquids having a pungent ethereal odor.
   [1913 Webster]

   Note: The ketones are named by adding the suffix-one to the
         stems of the organic acids from which they are
         respectively derived; thus, acetic acid gives acetone;
         butyric acid, butyrone, etc.
         [1913 Webster]

WordNet (r) 3.0 (2006):

ketone
    n 1: any of a class of organic compounds having a carbonyl group
         linked to a carbon atom in each of two hydrocarbon radicals