Definition of "air-tight"

Further along the gallery was the huge skeleton barrel of a brontosaurus. My museum hypothesis was confirmed. Going toward the side of the gallery I found what appeared to be sloping shelves, and clearing away the thick dust, I found the old familiar glass cases of our own time. But these must have been air-tight to judge from the fair preservation of some of their contents.

1895, H. G. Wells, chapter X, in The Time Machine

Spacecraft compartments can be isolated by air-tight doors in case of decompression. The cinematic version of explosive decompression is fiction; holed compartments either take enough damage that the occupants are killed instantly, or leak slowly enough that they are able to reach protective gear.

2008, BioWare, Mass Effect, Redwood City: Electronic Arts, PC, scene: Starships: Crew Considerations Codex entry