The Collaborative International Dictionary of English v.0.48:

Lactone \Lac"tone\, n. (Chem.)
   One of a series of organic compounds, being cyclic esters
   which may be regarded as anhydrides of certain hydroxy acids.
   In general, they are colorless liquids, having a weak
   aromatic odor. They are so called because the typical lactone
   is derived from lactic acid.
   [1913 Webster]