iTunes link: WordWeb Dictionary – Free
WordWeb is a handy English dictionary and thesaurus for your iPhone that covers 285,000 words and phrases as well as 225,000 word sense definitions. It includes both British and international English and gives you the ability to drill down on any word in a definition.
Unlike some other dictionary apps, it can function even when your phone doesn’t have an Internet connection available. It also has some neat features such as the ability to perform a fast pattern matching search where you can search using wildcards like * and ?. You can also bookmark individual definitions and view the history of your usage, plus there's a version of the dictionary with pronunciations as well as definitions for £2.39.
If you’re looking for a dictionary app to keep on your iPhone then this one is hard to beat.