资料来源 : pyDict

下垫层; 底垫; 垫底层

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

Underlayer \Un"der*lay`er\, n.
   1. One who, or that which, underlays or is underlaid; a lower
      layer.

   2. (Mining) A perpendicular shaft sunk to cut the lode at any
      required depth. --Weale.