The quality or state of being completely sealed so that air cannot escape or enter.
From 'airtight' plus the noun-forming suffix -ness. The compound 'airtight' became common in the 1800s as technology advanced.
Modern builders measure airtightness with specialized equipment called blower doors—improving a building's airtightness can cut heating costs by 20-30%, making this ancient concept of sealed containers suddenly very profitable.
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