[noun] - a first layer of paint that is put on a surface in order to improve the appearance of the final one, or the paint used for thisa tin of undercoat [U]Those red walls will probably need two undercoats. [U]Undercoats come in various colours. [C]Compare topcoat.
UNDERCOAT
Meaning of UNDERCOAT in English
Cambridge English vocab. Кембриджский английский словарь. 2012