Thanks to the excellent CGP Grey, I have learned that the notion that the Romans had rooms called vomitoria, where they could vomit out their meals so they could go back to eat more, is a myth. Some Romans apparently did engage in this practice, but there was no separate room devoted to it. Aldous Huxley, it seems, is generally credited — or debited? — with providing the first echo of this myth in a prominent English book, though the term must have been in the air for Huxley to have used it.
A vomitorium was, rather (in the words of the Oxford English Dictionary), a “passage or opening in an ancient amphitheatre or theatre, leading to or from the seats” (see, e.g., this reference). This dysphemism presumably stemmed from the analogy between people spewing forth through the openings and, well, …. Learn something new every day.