undercoat /ˈʌndɚˌkoʊt/noun 3verb 1forms 3 noun3 •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. — 2022 •A layer of short hairs underneath the longer ones of an animal's fur. •(no longer used) A coat for wearing indoors, under an overcoat. verb1 •To apply an undercoat to (something). formsundercoated · undercoating · undercoats