The phrase "crack book" means a book that is highly addictive and compelling to read. However, there are many different words that can be used as synonyms to describe the same phenomenon. For example, some people might call it a "page-turner," meaning that the book is so engrossing that it's hard to put down. Others might describe it as a "must-read," indicating that the book is essential reading for anyone interested in the genre. Still others might use the term "gripping" or "captivating" to describe a book that's hard to put down, while words like "riveting" or "spellbinding" suggest that the book is completely mesmerizing from start to finish.