Thednesday

Thednesday is the day in the week that is not really there. It doesn't occur every week, or most weeks for that matter. It doesn't even appear regularly; you can't say, "Did you know there's a Thednesday in two weeks?" But when it's Thednesday, you know. It's that day that makes it seem that the week is longer than it ought to be.* When you're, like, "It's only Tuesday?" that's because it's not Tuesday, it's Thednesday.
Today is totally Thednesday.

*For some reason, though, weeks with Thednesdays are no more productive than weeks without. I would venture to guess less productive, actually.