Which term describes a thin varnish used to finish wood?

The term that describes a thin varnish used to finish wood is shellac. Shellac is a natural resin that is dissolved in alcohol and used as a protective finish on woodworking projects. It provides a transparent coating that enhances the wood's appearance and provides a level of protection against moisture and wear.

Shellac is known for its quick drying time and ease of application, making it a popular choice for woodworkers looking to achieve a smooth and glossy finish. Additionally, it can be easily repaired or stripped if necessary, which adds to its appeal for finishing wood.

In contrast, the other terms don't pertain to wood finishing. Redress refers to addressing a remedy or a correction, rotund describes a round shape, and somniferous relates to inducing sleep. None of these have any association with the finishing process of wood, making shellac the clear and relevant choice.