'Undersoil' definitions:

Definition of 'undersoil'

From: WordNet
noun
The layer of soil between the topsoil and bedrock [syn: subsoil, undersoil]

Definition of 'Undersoil'

From: GCIDE
  • Undersoil \Un"der*soil`\, n. The soil beneath the surface; understratum; subsoil. [1913 Webster]