Veneering means

Veneering refers to the process of applying a thin layer of superior wood to an inferior wood substrate and bonding them together with adhesive. This technique allows for the enhancement of the appearance, durability, and quality of the underlying wood surface.

Carving out designs on timber planks is a separate woodworking technique and not related to veneering. Carving involves shaping or decorating wood by removing portions of the material using cutting tools.

Chemically treating timber planks involves applying chemical solutions to timber to improve its properties, such as resistance to decay, pests, or fire. It is not synonymous with veneering.

Thick layer of superior wood glued to inferior wood does not accurately describe veneering. Veneering typically involves applying a thin layer of superior wood to the substrate to achieve a desired aesthetic or functional effect.

Therefore, Option D: Thin layer of superior wood glued to inferior wood is the correct definition of veneering.