Doublebooked

(1) "Doublebooked" means a reservation (for a hotel room, for instance) which cannot be honored because the hotel promised it to more than one person.

(2) (Obsolete) (or "Doublebacked" or "tĂȘte-bĂȘche binding") Said of paperbacks, magazines, or fanzines, bound together heel-and-toe, so that each can be read from its cover inwards. The term came from Ace Books' use of this style for their paperbacks: "Ace Double Novels" (later "Ace Double"). Norman Spinrad suggested that Ace Books might someday republish and (as was the practice) retitle the Bible, as Wargod of Israel and The Thing With Three Souls.

from Fancyclopedia 2 ca. 1959
Of pbs or magazines, bound together heel-and-toe fashion so that each can be read from its cover inward. From Ace Books' use of this style for their pbs.