In the context of furniture, an onlay refers to a decorative element or embellishment that is applied onto the surface of a piece of furniture for ornamental purposes. It is typically made of wood, metal, or another material and is affixed to the furniture using glue or other fastening methods. Onlays are often intricately carved or molded to create visually appealing designs or patterns, adding a decorative touch to the furniture. Overlay. Decorative applique, as of veneers.