also air-tight
1.
If a container is ~, its lid fits so tightly that no air can get in or out.
Store the cookies in an ~ tin.
ADJ
2.
An ~ alibi, case, argument, or agreement is one that has been so carefully put together that nobody will be able to find a fault in it. (AM; in BRIT, use watertight )
Mick had an ~ alibi.
ADJ