Is there a configurable "word-of-the-day"-screensaver/ -widget
AFAIK - there's word-of-the-day screensaver that comes packed with every Mac OS X (since Tiger). You can configure it on a "per dictionary" basis. So if you need a limited list of some words, just create your own dictionary, install it on the system and I believe you'll be able to use it in a screensaver yourself.