Q: Does the iPad have a dictionary built in that I can use while reading iBooks?
– Marco
A: The specific features of the iBooks application have not yet been announced, although it’s important to note that the iBooks app will be a separate download from the App Store, as opposed to a built-in application.
This makes it possible for Apple to easily add new features to the application via updates, and also means that you certainly aren’t required to use the iBooks application—there are already numerous third-party ebook readers for the iPhone that should work fine on the iPad and will likely receive iPad-specific updates.
Many of these applications such as Stanza and eReader do in fact include dictionary features.