While working with Dictionary this weekend, I discovered that you can rename the dictionaries, as you can see in this screenshot:
To rename a dictionary, just Control-click on its name and choose Edit Label from the pop-up menu -- there's also a Revert to Original Label option, for when you decide the default names are fine. I'm not sure exactly why one might want to do this, though -- perhaps if you've installed another dictionary and want to give it a unique name?
Mac OS X Hints
http://hints.macworld.com/article.php?story=2008010706050630