EXAMPLES FROM THE WEB FOR UNDERCOAT
Like the beaver, it is furnished with an undercoat of soft downy fur.
Undercote, or undercoat; fester under the skin (coat is "cutis," skin).
This will act as a primer or undercoat for the succeeding coats of paint.
In the English method, where necessary, a priming or undercoat is employed.
Get some sort of stuff, made of sheep's clothing, I don't know what you call 'n, for to make an undercoat for the old oman.
The wiry coat sheds water like a duck's back, and the undercoat keeps him warm in all weather.
A fur seal naturally has fur, the hair seal has no undercoat whatever.
Many a smart blow was landed, but each perceived that the other wore an undercoat of linked mail which might not be pierced.