Veneer: A thin leaf or layer of a more valuable or beautiful material for overlaying an inferior one.
Veneers are used to layer type, functionality, or both, over existing types in a fine-grained manner. A veneer is often used to add that “final touch” to an existing, substantial type. It may also be a way to bind specific behavior to a simple type. Think of veneers as being a jar of fine polish in your cognizant-conversion toolbox.