http://schematix.com/wordflex/index.html
With more than 2 million language nodes for you to explore, The Wordflex Touch Dictionary is the next step in the evolution of the English dictionary and thesaurus.
Developed exclusively for iPad – in association with Oxford University Press – it's fun, fascinating and offers the first truly tactile, interactive reference for word lovers of all ages. It uses intuitive “mind-mapping” technology to turn word entries into dynamic trees that you can easily move, shape, rearrange, save and share with touch gestures.