Simple past tense and past participle of unbook.(verb)
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Use "unbooked" in a sentence
"This is the debt, yet unbooked, which is composed of the provisional claims of the creditors of the emigrants, the contractors, and various other holders of claims on the government."
"Hotwire is a hotel booking online service (also can get flights, and car rentals); when hotels have unbooked rooms, they sell them to Hotwire and Hotwire then gives you the customer a discounted deal – five-star hotel for a three star price (as their commercials say!)."
"Gosh that is funny about a horde of “the great unbooked” turning up for dinner, courtesy of the publishers?"