This plugin adds a widget that displays a random flash card from a Pauker data set and a second widget to display stats. See http://pauker.sourceforge.net/ for more details on Pauker.
Not sure whether it is appropriate to use a specific word in your blog. This plugin from BeeDictionary.com identifies difficult and confusing words and gives a small popup on hovering.
Supercharged tool to build your own awesome Encyclopedia / Lexicon / Glossary / Wiki / Dictionary / Knowledge base / Directory / Vocabulary in a breath.