Definition of "thin air" [thin air]

• An unknown location. (noun)

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• "Especially since I might see the people who now lived in my house—that “lovely” family that Mrs. Balicki the realtor had so conveniently produced out of thin air and had telephoned us about the night we finally came back from our joy ride with the Conways."
• "The red eastern sky, the northward blackness, the salt Dead Sea, the stony beach crawling with these foul, slow stirring monsters, the uniform poisonous-looking green of the lichenous plants, the thin air that hurts one's lungs: all contributed to an appalling effect."
• "It seemed to Inman that they were at the lip of a cliff, for the smell of the thin air spoke of considerable height, though the fog closed off all visual check of loftiness."