Snappy Words is a free online visual dictionary and thesaurus that requires no log in. Just enter a word

into the search box and this cool tool instantly creates a web of related words, definitions, and phrases.  Hover over any word in the web to view it’s definition. Double-click on a word, or drag a word to a new location to explore other branches of the word web. Snappy Words is simple, quick, and offers a visual alternative to the traditional dictionary.

Try it yourself at snappywords.com