ThinkMap Visual Thesaurus
The Visual Thesaurus is
“an interactive tool that allows you to discover the connections between words in a visually captivating display. Word maps let you search for just the right word and then explore related concepts, revealing the way words and meanings relate to each other. It’s a word-lover’s delight, with more than 145,000 words and 115,000 meanings organized in an innovative and intuitive design.” www.visualthesaurus.com
It does, however, require a subscription for more heavy use.