One of the things I really like about eReaders is the built in dictionary. Unfortunately, they aren't always comprehensive and, of course, fail when an author is making up new words.
So I came up with an improvement: eBooks should bundle a book-specific dictionary that can be merged with the standard dictionary while reading that book. This allows books to provide specific definitions of uncommon words and new words.
I'm re-reading The Lord of the Rings right now and Tolkien uses a lot of obscure and archaic words that are real (but which my eReader's dictionary doesn't know) and he also has a million made up words in Elvish, Dwarvish, Entish, "common tongue," etc. It would be helpful to be able to look those up as well.
So...Amazon, go make it happen.
Somebody does this...it was a shark tank deal. And links to related content etc. It was stupidly expensive per book though.