IPA: /ˈʌndərˌpeɪntɪŋ/
KK: /ˈʌndərˌpeɪntɪŋ/
A first layer of paint applied to a surface, usually in a single color, which serves as a foundation for additional layers of paint.
The artist started with an underpainting to establish the basic shapes and tones before adding more colors.
Underpainting is formed from "under-" (meaning beneath or below) and "painting" (from Old French *peint*, meaning to paint). The term refers to a preliminary layer of paint applied beneath the final layers in a painting process.
Think of a layer of paint that goes 'beneath' the final artwork — 'under-' means below, and 'painting' refers to the act of applying color.