This document features just over 400 possible vocabulary words for Warren St. John's Outcasts United. Sixty-five words that appear multiple times are noted as well. THIS PRODUCT IS JUST A LIST OF WORDS. The words are divided by sections and chapters. The Word document is editable.
You could ask students to highlight the words they don't know and build a class-determined vocabulary list from their responses. This is a great way to differentiate instruction.
If the book is a summer or independent read, the list could be an assignment where students define a specific number of words using the context of how/where the words appear in the book.