trapdoor

Short definition from Wiktionary

Noun

1. 1
   A hinged or sliding door set into a floor or ceiling.
2. 2
   Such a trap set into the floor of a stage to allow fast exits and entrances.
3. 3
   A secret method of obtaining access to a program or online system; a backdoor.
4. 4
   The special information that permits the inverse of a trapdoor function to be easily computed.
5. 5
   A door in a level for regulating the ventilating current; a weather door.

Verb

1. 1
   To subvert (a cryptographic scheme) by means of a secret parameter that makes the trapdoor function easy to compute.
2. 2
   To form a trapdoor deformity.