undercrust noun2 •A crust that forms the bottom of a pie, tart or other dish; a layer of pastry that supports the filling.In the middle ages, our forefathers found themselves deficient in plates and so, for a substitute, an undercrust of bread served as a plate. — 1919 •The layer of material located beneath the crust of a planet or moon.It must therefore form the undercrust of all Gallia. — 1878 formsundercrusts
