undercoat

noun

1. A layer of short hairs underneath the longer ones of an animal's fur.
2. A coat of paint or other material applied onto a surface before that of a topcoat; sometimes, a coloured primer.

   “The conversion process is carried out by Progress Rail at Longport, from where they are dispatched in undercoat to Eastleigh for final painting.”

3. (obsolete)A coat for wearing indoors, under an overcoat.

verb

1. (transitive)To apply an undercoat to.