Available from the Apple App Store (version reviewed), Play, and Amazon. This $2.99 version of this dictionary is all the dictionary you might need. Like any good dictionary, it provides a detail definition of the word, idioms, origin and even sample sentences.
Although I have not reviewed any other dictionary app, two features really stand out. The first one is the ability to do searches when offline. When I place the iPhone in Airplane mode, I am still able to search for words. Although I was no able to test it, it should work great for devices that don’t have permanent internet connections or where it is not permitted.
The second feature that I really liked (and probably not the intended purpose) is the ability to make a list of favorite words. My daughter receives a list of words weekly for a test at the end of the week, and it would be useful to have those definitions handy and quickly accessible throughout the week.
It also has many other features of various value. It has a built-in thesaurus, able to hear the word spoken out loud, search by voice (worked great for me), share the word via e-mail, twitter or Facebook (limited value), and word of the day in Spanish and English (not bad to increase your vocabulary).
My only complaints are that on the iPhone 4S it is slow sometimes especially clicking between the button navigational buttons, and that although I like the extra features the interface seems cluttered.
The $2.99 version has no ads except a more page where it promotes other apps.