trapdoor

UK/ˈtræpdɔː/US/ˈtræpdoɹ/

nounC1Very rare — outside the 30,000 commonest English words, so you will meet it in writing rather than in speechneutral

Other forms: trapdoors

A trapdoor is a hidden door set flat into a floor or a ceiling. You walk over it without noticing until it opens.

Theatres have them for entrances and disappearances, and the mechanism beneath a stage is a whole piece of Victorian engineering. Lofts, cellars and boats all use them. Fiction loves them for obvious reasons. There is a technical sense in cryptography, since a trapdoor function is easy to compute one way and very hard to reverse without a secret, which is what public-key encryption rests on.

Definitions of trapdoor

1nountrapdoorA hinged door set into a floor or ceiling.C1
“There was a trapdoor under the rug leading to the cellar.”

Where it comes from

From trap + door.

Etymology from Wiktionary, CC BY-SA

Practised in A Man Called Ove

First appears in chapter 3 of A Man Called Ove.

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trapdoor in the wild

In mathematical terms, if f is a trapdoor function, then there exists some secret information t, such that given f(x) and t, it is easy to compute x.
Trapdoor function
Here the key t is the trapdoor and the padlock is the trapdoor function.
Trapdoor function
Many members are known as trapdoor spiders due to their creation of trapdoors over their burrows.
Mygalomorphae
Ctenizidae is a small family of mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation, and silk.
Ctenizidae
The name comes from the distinctive behavior of the spiders to construct trapdoors, and ambush prey from beneath them.
Ctenizidae

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From Wikipedia, CC BY-SA 4.0. These sentences were written by other people about their own subjects; they are here to show the word at work, not as anybody’s opinion.

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