Your linguistic trivia for the day, via, of course, Unfogged. I've always been aware of that class of words that are their own opposites ever since reading something in Reader's Digest as a kid or teen, but I couldn't remember the exact term for them, and the only example I could ever think of was "buckle."
Yes, I read Reader's Digest as a kid. Don't judge me! My parents had a subscription, and I read it mostly just for the jokes. To the extent that I ever flirted with right-wing ideas, I blame mostly that magazine, but it was partly P.J. O'Rourke's fault too.