Could you hint the best etymology book?
I'd like to learn new words via their origin.
Norman Lewis: Word Power Made Easy is one of the best books.
There is no best book.
Parts of this book are available on line:
Gold, David L. 2009. Studies in Etymology and Etiology (With Emphasis on Germanic, Jewish, Romance, and Slavic Languages). Selected and edited, with a foreword, by Félix Rodríguez González and Antonio Lillo Buades. Alicante. Publicaciones de la Universidad de Alicante.
On reflection, I realize that you need something other than a book on etymology.
If you have in mind expanding your vocabulary (by learning words coined at any time in the past or now), you need a book that will give you the meanings of prefixes and suffixes that are used to form words.
Try this one:
Robert Schleifer's Grow Your Vocabulary By Learning the Roots of English Words
If you have in mind expanding your vocabulary by learning newly coined words, try this
Barnhart Dictionary of New English (at least three volumes)
The Barnhart Dictionary Companion