The opposite of hyperbole is understatement, which isn't exaggeration in the sense of making something bigger than it is, but we could argue that you can exaggerate smallness too, yes? For that we have a cool technique called litotes (LYE-teh-teez), an indirect statement that dampens the impact of something by negating its opposite or making light of the truth. He's not too swift. Wrapping your car around that tree didn't do much for the front end. And perhaps my all-time favorite, which I heard at work years ago, She's just a little pregnant around the edges.
Apophasis(ah-PAHF-ah-sis) is understatement that states something by stating it will not be stated. These are all your "needless to say," "I don't need to tell you" and "as you undoubtedly know" remarks. Like all understatement, it's meant to get a point across in a delicate, persuasive, wryly humorous, or inoffensive manner, giving directions yet expressing your confidence that the person already knows as much. Then again, apophasis can signal an antagonist that your words have teeth while still remaining pleasant: For the moment we'll overlook any rumors that you blew the entire month's payroll at the casino.
Well, I'd better go make supper before everybody starves to death. Such an event wouldn't exactly make our families' weekend. Needless to say, I'll expect some comments on this post. :)