undercoat

noun

1.
seal consisting of a coating of a tar or rubberlike material on the underside of a motor vehicle to retard corrosion
underseal
Derived from:
undercoat
2.
the first or preliminary coat of paint or size applied to a surface
flat coat ground primer primer coat priming priming coat
Derived from:
undercoat
3.
thick soft fur lying beneath the longer and coarser guard hair
underfur