Not a dictionary at all (by any definition that I can find), but a whole new and brilliant tool for finding spellings. The key is in the organisation with an index giving access to manageably sized word lists. But the book isn't just a list of words, it also contains advice on how to learn the correct spellings.
My ten year old son has specific spelling difficulties and has become very negative about the whole trial of spelling tests and the pain of learning. Last week we introduced him to this book and within minutes he had a taste of what he could do with it. A couple of days later he was actually asking to play scrabble (using it as an aid). Today he went looking for it to take to school.
Obviously this is a tool, not a miracle cure but it is the first of the many we have used (rote learning, look/cover/write, SOS etc.) that has fundamentally changed my son's attitude to spelling.
Why not five stars? Only that we haven't had the book for long and the I am reserving the fifth star for the long term impact on my son's spelling. Given the start, I expect the book to earn it.