Trapdoor /(?)/

Trap·door

Trapdoor

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

Phrases & Compounds
Trapdoor spider
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).