undercoat (Noun) — Seal consisting of a coating of a tar or rubberlike material on the underside of a motor vehicle to retard corrosion.
undercoat (Noun) — The first or preliminary coat of paint or size applied to a surface.
undercoat (Noun) — Thick soft fur lying beneath the longer and coarser guard hair.
undercoat (Verb) — Cover with a primer; apply a primer to.