I. ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ noun
Etymology: under (III) + coat
1. : a coat or jacket formerly worn under another
2. : a growth of short hair or fur partly concealed by a longer growth
a dog's undercoat
3.
a. : a coat of paint under another
b. : a paint prepared for use under a finishing coat
red lead undercoat
c. : ground coat 2b
4. Britain : the course of crushed stone that is immediately under the wearing surface of a bituminous pavement
5. dialect : petticoat
II. transitive verb
1. : to apply an undercoat to
undercoat steelwork with a primer
2. : to apply a special waterproof coating to the undersurfaces of a vehicle