Well, duh...

From the Things-I-never-thought-of-but-make-perfect-sense files:

The vomitorium was not, as urban legend has it, a room for ancient Romans empty their stomachs, so to speak; it was a passage that allowed play or sporting-event spectators to exit an ampitheater quickly.

If you clink through, you'll discover that we now shorten vomitorium to "vom" for a theater exit, often in front of the proscenium.

Who'd a thunk it?

I used that term for years w/o having any sense of its history...