Okay, so I have an open question for the linguists on E2. I'm putting this here because I don't know where else to put it.

Is there a term for a single phrase that signifies two opposite ideas?

Some examples (all from Shakespeare):

1. "When we have shuffled off this mortal coil" (there is tension here between one meaning of the phrase, "When we have cast off this burden of life," and the fact that a snake rejuvenates itself whenever it "shuffles off" its "coil")

2. "There's husbandry in heaven, their candles are all out" (on the one hand an Elizabethan husband was responsible for snuffing "out" candles to conserve them; on the other, he was also responsible for making sure that all of the candles in the house were lit. The phrase is further complicated by the fact that "candles" are here used as metaphors for stars, which are often described as "out" when present)

3. "To die, to sleep, no more" -- 1. "To die is nothing more than to sleep" and 2. "To die is to sleep no longer."

4. "Oh you are men of stones." -- 1. "Oh, you are stones." and 2. "Oh, you are men of stone."
EDIT: anthropod says re May 4, 2006: Contronym does it for words.

I wonder if the term can be applied to phrases, though...