Other forms: overlaid; overlaying; overlays; overlayed
To overlay is to cover with a coating or a layer, or to set one thing on top of another. A winter storm will sometimes overlay a dangerously slick coating of ice on top of the road.
An artist might overlay a ceramic object with gold, or overlay one piece of paper on another in a collage. The layer itself, whether it's clear plastic or cement or silver, is also called an overlay. Another kind of overlay, dating from the 1930s, is the transparent sheet of paper in a book that covers a map or other full-page illustration.