Late to the show, I stumbled upon Visual Thesaurus, a kind of interactive mind-mapping tool. It was invented by Marc Tinkler of New York-based Thinkmap at a time when swissmiss was design director with his firm.
"I got to brand The Visual Thesaurus, shape the user interface of the actual app, do the first version of their site, and work on all marketing material. It was my last big project before I left and went out on my own and also one of the most exciting projects I have ever worked on in my career."
— Tina Roth Eisenberg
(From an interview with Tina on The Great Discontent.)
Visual Thesaurus now contains more than 145,000 English words and more than 115,000 meanings. You can listen to British and American pronunciations, and there are beta versions in five European languages, too.
It's subscription-based, but you can test it for free.
A great reference tool.