Kindle for iPhone and iPad App v2.2 brings full dictionary in it. "Now in the Kindle app when you highlight a word, a definition automatically appears at the bottom of the screen, alongwith links to search the word on Google or Wikipedia. The feature also includes a link for "Full Definition" of highlighted word. Clicking the link take you to new Oxford American Dictionary that's automatically downloaded in v2.2, and contains some 250,000 entries," Amazon informs.
The latest iPad version of Kindle app also allows you to search inside a book. And, this too matches iBooks functionality. The in-book search for iPhone has also been improved with 2.2. Other small improvements include better line spacing on the iPad version, and fast-app switching for iOS 4 devices.