Robert Scheiner has Wordflex Touch Dictionary (iTunes Link) for the iPad in the iTunes App Store for FREE (regularly $11.99) for a limited time.

Developed exclusively for iPad and with rich content from the Oxford University Press, this fun, fascinating tool offers a truly engaging reference for word lovers of all ages and interests. By using your fingers to manipulate word trees, you will experience language as an interactive adventure, and will find information quickly and easily.