"Origins: An Etymological Dictionary of Modern English" by Eric Partridge
A "must have" book.
If you love the English language and are truly very curious about the meanings of its words as reflected in the evolution of its origins and meanings, this is a "must have" book. I have used the 1966 issue of it for years now, and rate it more useful, although a companion book, to the seminal work of Walter Skeat. No library can realistically be said to be complete,nor can any lover of the English language, without both of these works.