First coined by Richard Lederer in the late 80s, contronyms are a whole lotta fun. I've also read that they're called antagonyms, as well. However you want to call "˜em, the basic idea is this: one word that has two meanings which are fairly opposite one another.
An example? Sure, why not: the word cut can mean both to get out of ("We cut school") and to get into ("We cut in line").
Another good one: release. On the one hand, it means to set free and on the other hand, it means to sign up for another lease, as in "We are re-leasing the apartment from our schmuck of a landlord even though he raised our rent yet again."
Yet another: left. If you leave the party early, you've left. But if you're the only loser who remains, you're the only one left.
Lastly: anxious. You can either be all stressed out now and outta whack with fear about the immediate future (because any Word Wrap devotee knows what's coming next), or you can be totally looking forward to showing off your smarts by leaving your own contronym in the comments below.