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Webster 1913 Edition

Adj.

So tight as to be impermeable to air or other gases;

as, an

air-tight

cylinder

; – said of containers.

Noun.

A stove the draft of which can be almost entirely shut off.

[Colloq. U. S.]

See also: airtight and air tight

air-tight ‎(comparative more air-tight, superlative most air-tight)

Alternative form of airtight
- 1895, H. G. Wells, The Time Machine Chapter X
  Further along the gallery was the huge skeleton barrel of a brontosaurus. My museum hypothesis was confirmed. Going toward the side of the gallery I found what appeared to be sloping shelves, and clearing away the thick dust, I found the old familiar glass cases of our own time. But these must have been air-tight to judge from the fair preservation of some of their contents.