Source : Webster's Revised Unabridged Dictionary (1913)

Interpenetrate \In`ter*pen"e*trate\, v. i.
   To penetrate each the other; to penetrate between bodies or
   their parts.

   {Interpenetrating molding} (Arch.), in late Gothic
      architecture, a decoration by means of moldings which seem
      to pass through solid uprights, transoms, or other
      members; often, two sets of architectural members
      penetrating one another, in appearance, as if both had
      been plastic when they were put together.