\Sub"soil`\, n.
The bed, or stratum, of earth which lies immediately beneath
the surface soil.
{Subsoil plow}, a plow having a share and standard but no
   moldboard. It follows in the furrow made by an ordinary
   plow, and loosens the soil to an additional depth without
   bringing it to the surface. --Knight.

\Sub"soil`\, v. t.
To turn up the subsoil of.