airtightcap
nounUK /ˈeətaɪt kæp/
US /ˈerˌtaɪt kæp/
A cap that does not let air or water get in or out.
She screwed the airtightcap onto the bottle so the juice would not spill.
OTHER MEANINGS
2. A cover that keeps food fresh by blocking air.
The airtightcap kept the cookies crunchy for a week.
3. A lid used on a container to stop leaks.
He put an airtightcap on the paint can before shaking it.
4. A top that seals a tube tightly.
The glue dried out because the airtightcap was left off.