Source : Webster's Revised Unabridged Dictionary (1913)

Air-tight \Air"-tight`\, a.
   So tight as to be impermeable to air; as, an air-tight
   cylinder.

Air-tight \Air"-tight`\, n.
   A stove the draft of which can be almost entirely shut off.
   [Colloq. U. S.]

Source : WordNet®

air-tight
     adj 1: having no weak points; "an airtight defense"; "an airtight
            argument" [syn: {airtight}]
     2: not allowing air or gas to pass in or out [syn: {airtight},
        {gas-tight}]