Amazon's X-Ray for the Kindle App is now available for Android. X-Ray basically offers encyclopedic knowledge of whichever book you are reading. Whenever you click the X-ray button somewhere on the app's top bar, it can display particular terms and their meaning, or a list of characters and the parts of the book they appear in, or significant phrases appearing throughout the text and more.
X-Ray will work for novels or text-books, which means it can help you in your schoolwork too. This new version even includes some additional useful features like push notifications and the ability to make flashcard sets. Here's a quote with a description from the Google Play Store for all the details,
The Kindle app puts over a million books at your fingertips. It’s the app for every reader, whether you’re a book reader, magazine reader, or newspaper reader—and you don’t need to own a Kindle to use it. Choose from over a million Kindle books from the Kindle Store or enjoy popular magazines like The Economist and Reader’s Digest with high-resolution color images.*
• Read Free Books—Choose from thousands of free ebooks such as Pride & Prejudice or The Adventures of Sherlock Holmes.
• Shop for Books—Easily shop for ebooks, including new releases and New York Times Best Sellers.
• Use the Built-In Dictionary, Google, and Wikipedia—The Kindle app has a built-in dictionary that allows you to look up words instantly while you’re reading your ebooks. Simply tap and hold a word to view its definition or use the Google and Wikipedia links to get more information.
• Sync Your eBooks—The Kindle app lets you read the same book across devices and automatically syncs where you left off so you can start reading on one device and pick up where you left off on another device. The app syncs your furthest page read, bookmarks, notes, and highlights between Android, PC, Mac, iPad, iPhone, iPod touch, BlackBerry, Windows Phone 8, and any of our Kindle devices using our Whispersync technology.
• Sample Books Before You Buy—Read the first chapter of a book for free before you decide to buy.
• Customize Your Reading—Choose your preferred font size, screen brightness, background color, and orientation (portrait or landscape) to read your books.
• Borrow eBooks from the Library—Check out ebooks from your local library and have them delivered wirelessly to your Kindle app.
• Read print replica textbooks on Android tablets. Print Replica Kindle books maintain the rich formatting and layout of their related print editions and provide features to help students study smarter including ability to highlight passages, add margin notes, and search for keywords. Whispersync technology saves and synchronizes your bookmarks, notes, and highlights across your devices.
* Selection for U.S. users only; selection and price of ebooks and e-periodicals vary by country.
It's free on the Google Play Store: Amazon Kindle - Android Apps on Google Play