the first coat of paint, especially the initial painting on a canvas in which the major areas, tones, colors, and forms are indicated in mass.
Origin of underpainting
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
the first layer in a painting, indicating the design and main areas of light and shade
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012