UNDERSEAL

undercoat, underseal

(noun) seal consisting of a coating of a tar or rubberlike material on the underside of a motor vehicle to retard corrosion

Source: WordNet® 3.1

Etymology

Noun

underseal (plural underseals)

A thick, resilient coating applied to the underbody or chassis of an automobile to protect against damage from small stones, etc, which would rapidly chip ordinary paint and allowing rusting to begin.

Verb

underseal (third-person singular simple present underseals, present participle undersealing, simple past and past participle undersealed)

(transitive) To coat (the underbody or chassis of a vehicle) with underseal.