Eric Partridge 
Origins [PDF ebook] 
A Short Etymological Dictionary of Modern English

This etymological dictionary gives the origins of some 20, 000 items from the modern English vocabulary, discussing them in groups that make clear the connections between words derived by a variety of routes from originally common stock.

As well as giving the answers to questions about the derivation of individual words, it is a fascinating book to browse through, and includes extensive lists of prefixes, suffixes, and elements used in the creation of new vocabulary.