Source : Webster's Revised Unabridged Dictionary (1913)

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}).