Definition of polyfill:
(n) :
(web development) A plugin that provides the functionality of newer browsers to older versions.
(n) :
A synthetic textile used for bulk or insulation, e.g., in stuffed animals or coats.
(n) :
(computer graphics) An algorithm to fill a polygon with a particular color.
(v) :
(web development, transitive, intransitive) To create or apply a polyfill.