Greg Pierce, the same guy that brought my beloved Drafts, has released a new version of his dictionary/word sleuthing app, Terminology. Terminology 3 is a ground-up rewrite for iOS 7. In addition to a built in dictionary/thesaurus, Terminology searches across the web and other apps which support integration. It includes iOS sync between your devices and extensible via URL scheme.
Terminology is a great writing tool and now it looks great on iOS 7. It's $2.99 and universal for the iPad and iPhone.