Airlock

Part of speech: noun

Definitions

1. A sealed chamber with two or more doors that allows passage between spaces of different pressures or atmospheric conditions while preventing direct exchange between them
2. A specialized enclosure designed to control entry and exit between environments with varying air pressures or atmospheres, ensuring that one space remains isolated from the other
3. This structure contains at least two doors that function to permit transitions between areas of distinct atmospheric conditions while maintaining separation to avoid direct mixing

Etymology: "Airlock" is a plain compound of "air" and "lock," and the pairing reads almost literally: a lock that controls air. A lock, in the older sense of a closed-off section of a waterway or a secured door, keeps one space separate from another, and an airlock applies the same principle to pressure rather than water or people. Two doors are never open at once, so the chamber between them can be pressurized or depressurized to match whichever side a person or object is passing from. The idea predates the word's most famous use. Spacecraft and submarines are the settings where airlocks matter most, since a sudden loss of pressure there can be fatal, but the principle is an engineering one that the name describes directly rather than through metaphor.