Merriam-Webster's Collegiate® Dictionary, 11th Edition
OVERLAY
I. transitive verb (overlaid; -laying)
Date: 14th century
1. to lay or spread over or across ; superimpose , to prepare an overlay for, overlie 2,
II. noun
Date: 1794
a covering either permanent or temporary: as, an ornamental veneer, a decorative and contrasting design or article placed on top of a plain one, a transparent sheet containing graphic matter to be superimposed on another sheet