Trapdoor \Trap"door`\, n.
   1. (Arch.) A lifting or sliding door covering an opening in a
      roof or floor.
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   2. (Mining) A door in a level for regulating the ventilating
      current; -- called also weather door. --Raymond.
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   Trapdoor spider (Zool.), any one of several species of
      large spiders which make a nest consisting of a vertical
      hole in the earth, lined with a hinged lid, like a
      trapdoor. Most of the species belong to the genus
      Cteniza, as the California species (Cteniza
      Californica).
      [1913 Webster]