资料来源 : pyDict

底层

资料来源 : Webster's Revised Unabridged Dictionary (1913)

Understratum \Un"der*stra`tum\, n.; pl. L. {Understrata}, E.
   {Understratums}.
   The layer, or stratum, of earth on which the mold, or soil,
   rests; subsoil.