An intelligently pared-down dictionary and thesaurus app, Ninjawords will make you feel and seem slightly less dumb. It works offline, too.
Some other dictionary apps have more features—or rather, more feature bloat—but anything you might miss, like traditional pronunciation guides, is made up for by how quickly you'll find what you're looking for.
From the App Developers: Ninjawords is the simple, fast and deadly dictionary for the iPhone.
Ninjas are three things:
1. They're smart
2. They're quick
3. They're deadly accurate
Ninjawords was built on these principles.