subsoil

As a noun subsoil

is the layer of earth that is below the topsoil.

As a verb surface is

.

As a noun subsoil

is the layer of earth that is below the topsoil.

As an adjective undefined is

lacking a definition or value.

As nouns the difference between subsoil and subsurface

is that subsoil is the layer of earth that is below the topsoil while subsurface is something that is below the layer that is on the surface.

As an adjective subsurface is

below the surface.

As nouns the difference between subsoil and stonebrash

is that subsoil is the layer of earth that is below the topsoil while stonebrash is a subsoil made up of small stones or finely broken rock.

As nouns the difference between subsoil and understratum

is that subsoil is the layer of earth that is below the topsoil while understratum is the layer, or stratum, of earth on which the soil rests; the subsoil.

As nouns the difference between subsoil and subsoiler

is that subsoil is the layer of earth that is below the topsoil while subsoiler is a type of plough that loosens the subsoil.

As nouns the difference between subsoil and solonetz

is that subsoil is the layer of earth that is below the topsoil while solonetz is a type of soil with a so-called "natric horizon" within the upper metre of the soil profile and a subsoil with higher clay content than the upper horizon, the latter having more than 15% exchangeable sodium.