thumb|A trapdoor to a [[bomb shelter from World War II]]
A trapdoor or hatch is a sliding or hinged door that is flush with the surface of a floor, ceiling, or roof. It is traditionally small in size. It was invented to facilitate the hoisting of grain up through mills, however, its list of uses has grown over time. The trapdoor has played a pivotal function in the operation of the gallows, cargo ships, trains, booby traps, and more recently theatre and films.
History
thumb|Deck hatch of the [[Omega (barque)|Omega, the last square-rigged sailing cargo ship]]
Originally, trapdoors were sack traps in mills, and allowed the sacks to pass up through the mill while naturally falling back to a closed position.
Railways
The term trapdoor also refers to a plate in the entry vestibule of a passenger railcar that permits access to high-level platforms when lying flat against the floor of the car, and which can be flipped open to expose steps for accessing ground-level platforms. Many American commuter railroads which operate the Comet railcars made by Bombardier have trapdoors to accommodate passengers boarding and alighting on both high-level and ground-level platforms. Amtrak's Viewliner, Amfleet, and Horizon railcar fleets all have trapdoors.
Biology
Trapdoor spiders hide in an underground nest they line with their silk, and then conceal it with a hinged silk lid, the trapdoor.
Star traps in theatre
thumb|220px|19th century Star trap from the [[Theatre Royal, Drury Lane, London, Now at the Victoria and Albert Museum]]
In theatrical use, "star traps" allowed extremely fast appearances on stage, such as jinn appearing in a puff of smoke.