What does airlock mean?
An airlock is a sealed compartment fitted with two airtight doors, allowing people or materials to pass between environments held at different pressures without disturbing either one. When someone enters an airlock, the inner door closes, the chamber's pressure adjusts, and only then does the outer door open — a sequence familiar from spacecraft, submarines, hyperbaric chambers, and sterile clean rooms. The word also has a second life in homebrewing, where a small plastic airlock vents fermentation gases while blocking airborne contaminants. The term carries a technical, scientific register and evokes precision engineering and safety protocols. It is a genuinely useful word for anyone writing about space exploration, diving, or industrial processes, capturing in a single noun the elegant principle of moving between worlds without letting them mix.
A small chamber with airtight doors at both ends that permits passage between areas of different air pressure without equalizing them.
"Crew members must cycle through the airlock before every spacewalk."
Common in aerospace, diving, and clean-room contexts.
A one-way valve used in fermentation vessels to release carbon dioxide while preventing outside air and contaminants from entering.
"Bubbling in the airlock showed that fermentation was active."
Standard pluralization; used when referring to multiple chambers or valves.
"The space station has several airlocks for crew and cargo transfers."
Without an airlock, stepping outside a spaceship would vent the entire cabin into space — it's the humble doorway that makes spacewalking possible.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of airlock
The word airlock combines 'air', from the Greek-derived element 'aer' via Latin and French, with 'lock', from Old English 'loc', meaning a fastening or enclosure. It emerged as a technical compound in the nineteenth century as engineers developed pressurized tunnels, caissons, and diving equipment, and it gained widespread recognition during the space age when airlocks became essential to human spaceflight.
How airlock is actually used
The term is most strongly associated with aerospace, diving, and laboratory contexts; in homebrewing circles 'airlock' refers specifically to the fermentation valve, a distinct but commonly encountered sense.
Easily confused with airlock
An airplane is an aircraft that flies through the air, whereas an airlock is a sealed passage chamber that controls pressure differences between two environments.