Undercoat (noun)

1. A coat applied as a base coat before the finish coat.
2. A layer of paint, varnish, or similar material applied as a primer before the final coating.
3. A layer of fur or hair on the body of an animal that is covered by the longer outer coat.

Origin:

Late 19th century: from under- + coat.

Examples:

1. He applied an undercoat of paint to the walls before applying the final color.
2. The dog's thick undercoat protected it from the cold weather.
3. The undercoat is an important step in preparing the surface for painting.
4. The undercoat of paint will help the final coat adhere better.
5. The undercoat of the animal is shed seasonally.