Every so often a free app comes along for the iPhone/ iPod touch that I think everyone should have. That certainly applies to Dictionary.com [App Store link]. It's an iPhone version of the Dictionary.com web site which gives you definitions, a thesaurus, audio pronunciations, and my favorite, word origins. (I was interested to learn that the word 'waver' goes back to the 13th century German word for moving about. I love stuff like that.) The app also provides a word of the day, and examples of your specified word in sentences.
This app is every bit as good as the paid dictionary apps, and oh so more versatile. Happily, Dictionary.com does not need an internet connection for the dictionary and thesaurus, but does need it for the rest of the features. With all that information on board, the download is about 36 megabytes.
As you type a word, the dictionary auto-completes, saving you some time, and when you go back to your 'recents' list you have a choice of seeing the thesaurus or the dictionary. Nice. Pronunciations of the words are quite handy. Sometimes you get a female voice, other times a male.
One small nitpick. You should be able to click on words that the thesaurus finds and get a definition. You have to retype them.
Dictionary.com was released in late March, and I don't think the word is out sufficiently so people know it is there. Consider this the 'word', and consider the occasion a propitious one. Look it up.