Also, courtesy of Wikipedia's daily email, the Names of Istanbul page. It turns out that the official renaming from "Constantinople" to "Istambul " only happened officially in 1930, much later than I had thought. On the other hand, "Istanbul" is a variant of the Turkish for, literally, "The City", and had been the informal name in Turkish for the city since even before 1453 (and, in Greek, even before that).
Istanbul means "The City." And it has been called "the city" for a long time regardless of the language.
I'm oversimplifying and focusing on a very narrow slice of a complex and certainly ambiguous history, but, gods, isn't that something?