Geez. I feel really dumb. I read the post, thought about it, and replied with the first word that came to mind, and didn't even realize that it was the title of the thread. So maybe that tells you that if you picked is as the title and it was the only word that came to me after Mr. M's oxymoron," it's the right word.
The only other words I can think of are dichotomy or paradox.