Is there a word for words or phrases that have two, contradictory meanings? For example, "draw the curtains" can mean both open and shut the curtains. The "shank of the evening" can be both the early part and the late part of the evening.

"Double entendre" springs to mind, but that is usually two intentional meanings. How about "equivocal" or "bifarious"?

www.podictionary.com the audio word-a-day

You might want to double-check this (I'm on a borrowed computer and don't want to look it up right now) but I believe the word is contranym.

here's a quote from our own Anu Garg:

I call them fence-sitters. They sit on the fences, ready to say one thing or its opposite, depending on which side they appear. I'm not talking about politicians. These are words, known by many names: autoantonym, antagonym, contranym, enantiodromic, amphibolous, Janus word, and so on.

actually, that middlish one should be enantiodrome (and I suppose the next is amphibole), to maintain noun forms.