What does airtight mean?
"Airtight" is an adjective with two closely related senses. Literally, it describes something sealed so completely that air cannot enter or escape — an airtight jar keeps coffee fresh, and an airtight seal prevents leaks in machinery or buildings. Figuratively, it describes anything so well-constructed that it cannot be faulted: an airtight argument, an airtight contract, or an airtight alibi leaves no loopholes and admits no counterattack. The word pairs "air" with "tight," and its figurative meaning grew naturally out of the physical idea of perfect sealing. It is a standard term in both British and American English, appearing everywhere from kitchen instructions to courtroom drama. Its connotations are strongly positive, suggesting thoroughness, rigor, and reliability. Related terms include "watertight," which emphasizes water rather than air but shares the same figurative sense of flawlessness. Few everyday adjectives move so smoothly between the pantry and the courtroom, which makes "airtight" a compact and vivid way to describe absolute security against intrusion, escape, or error.
Sealed so completely that no air can enter or escape.
"Keep the biscuits in an airtight tin so they stay crisp."
Most often applied to containers, packaging, seals, and enclosed spaces.
(Figurative) Having no weaknesses, flaws, or loopholes; impossible to dispute or escape.
"The prosecution built an airtight case over three years of investigation."
Commonly used of arguments, contracts, plans, defenses, and alibis.
Lawyers don't just want a good argument — they want an 'airtight' one, a phrase borrowed straight from the world of sealed containers where not even a molecule of air gets through.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of airtight
"Airtight" is a compound formed from "air" (ultimately from Greek "aēr," via Latin) and "tight" (from Old Norse "téttr," meaning dense or firm), joined in English during the late eighteenth century as industrial sealing technology advanced. The literal sense came first, describing containers and vessels closed against air; the figurative sense of an unassailable argument developed later by natural extension. The compound follows the same pattern as the older "watertight," which served as its model.
Related word forms
How airtight is actually used
Both senses are common in everyday English. The literal sense appears mostly in contexts of food storage, packaging, and construction, while the figurative sense is especially frequent in legal, journalistic, and detective writing. The figurative use carries a positive connotation of rigor and reliability.
Easily confused with airtight
Watertight means sealed against water specifically, while airtight means sealed against air; both are used figuratively to mean flawless, but airtight is more common for arguments and alibis.