I have and like one by Flow Simulation, Ltd., and I haven't found it for Win 8. It's called English Dictionary for Windows
phone 7.1 (yes, 7.1). I have a Version 3.7 running on Mango (7.5), FWIW. Very nicely designed app with truly helpful, interesting, and instructive search features. This dictionary is one reason I still keep my now-Wi-Fi-only Focus charged and ready.
Edit: I was wrong; I did just download it for my 1020. It's the second one listed at the Store when you search for "dictionary".