Trapdoor \Trap"door`\, 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. --Raymond.

Trapdoor spider (Zo["o]l.), 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 (C. Californica).

Source: Webster's Revised Unabridged Dictionary (1913)