Trapdoor

n.
  1. (Arch.) A lifting or sliding door covering an opening in a roof or floor.
  2. (Mining) A door in a level for regulating the ventilating current; -- called also weather door.
    3. Trapdoor spider (Zoöl.),
    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).