Moritz has been working on visualization of a hierarchical glossary carefully named "Glossary Visualization" versions 2-5. Not sure where version 1 is. Being a network graph, I can see this getting chaotic when there are more words (or categories) involved, but then again, maybe that's all the words. In either case, it beats browsing through words in a dictionary; although, these prototypes don't include definitions yet.
In the most recent version, words are represented as a DOI tree showing only the categories. Click on a category and view the sub-categories.
All four versions were implemented using the recently-mentioned Flare visualization toolkit.
What do you think - cluttered or just right?