Lactone

A lactone is a type of organic compound. A chemical is a lactone if it has a ring of atoms (it is cyclic) including an ester group (an oxygen atom next to a carbonyl). A structural systematic name of this group (without any other groups attached) is 1-oxacycloalkan-2-one.

The name "lactone" comes from the chemical now called lactide. Lactide was made from distillation of lactic acid, like acetone was made from acetic acid, so it was called "lactone".From p. 1223:  "Indépendamment de la lactide dont je viens de rappeler l'existence dans les produits de la distllation de l'acide lactique, celui-ci donne encore, par sa décomposition, une autre substance, que je propose d'appeler lactone, parce qu'elle me paraît être à l'acide lactique ce que l'acétone est à l'acide acétique."  (Independently of the lactide of which I have just recalled the existence in the products of the distillation of lactic acid, this [i.e., lactic acid] gives further, by its decomposition, another substance, which I propose to call lactone, because it seems to me to be to lactic acid what acetone is to acetic acid.)
  Reprinted:   ; see p. 262.
  English translation:   ; see p. 31.
   The name was later used to mean anything with the cyclic ester structure.

 Sources 

Lactones
Category:Functional groups