trapdoor

A hinged or sliding door set into a floor or ceiling.

Such a trap set into the floor of a stage to allow fast exits and entrances.

A secret method of obtaining access to a program or online system; a backdoor.

The special information that permits the inverse of a trapdoor function to be easily computed.

A door in a level for regulating the ventilating current; a weather door.

To subvert (a cryptographic scheme) by means of a secret parameter that makes the trapdoor function easy to compute.

To form a trapdoor deformity.