*trapdoor*

n. 1. (Arch.) A lifting or sliding door covering an opening in a roof or floor. [ 1913 Webster ]

2. (Mining) A door in a level for regulating the ventilating current; -- called also weather door. Raymond. [ 1913 Webster ]

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 ]