airlock

IPA: ˈɛrɫɔk

A sealed, airtight chamber, such as in a manned spacecraft or submarine, used to provide access to and from the sealed area without allowing air out or water in.
(architecture, informal) A vestibule, foyer or entranceway with doors to the exterior on one end and doors to the interior on the other, functioning to keep indoor and outdoor air, humidity, and air temperatures separate.
Alternative form of air lock [A small amount of air in a pipe that stops liquid flowing through it.]

air lock

IPA: ˈɛrɫˈɑk