Etymology, the study of the historical derivation of words from their sources in older or in other languages, is the most important of sciences for the true student of language. In English there are Calvert Watkins' Dictionary of Indo-European Roots, Reverend Skeats' Concise Dictionary of English Etymology, and Shipley's discursive Origins of English Words. For the classical languages there is Buck's Comparative Grammar of Greek and Latin.
And now there is Brodsky's Spanish Vocabulary: An Etymological Approach.
No, his work is not encyclopedic. There are many words such as 'milagro' or 'sapo' or 'pendejo' with which intermediate speakers of Spanish will be familiar for which he provides no etymology. But Brodsky's intention is to widen your Spanish vocabulary as a whole within two contexts, the classical roots of the language, and your knowledge of cognate words that already exist in English. To that end he does address over 5,000 Spanish words, giving for most their corresponding roots in Latin (or Greek, Germanic, Arabic, etc.) and their counterparts in English where they exist. Brodsky's goal is to help broaden your vocabulary not by arbitrary memorization but through making clear the association of new words with words you already know. What results is a painless, educational, and often quite diverting introduction to the etymology of both English and Spanish and a history of the development of Western thought in the last two millennia to boot. Would you, for example, guess that the common Spanish word 'lástima' has the same unlikely root as the English word 'blame,' both being vulgar (i.e., common and unlearned) developments from the Greek 'blasphemia'?
This book is a wonderful accomplishment. It presents an amazing amount of data in an attractive and approachable format. It should not intimidate anyone with an intermediate knowledge of Spanish. Neither will it disappoint the advanced student as a reference. Greek and Arabic forms are treated matter-of-factly in a Latin alphabet transcription. And while no knowledge of the classical languages will be necessary, serious students of Greek and Latin will not feel condescended to. And this is not a dry work. There are plenty of asides such as a short essay on the common origins of the English word 'bigot' and the Spanish word for moustache which add to the text immensely. The author obviously loves his subject.
This is an ideal book. It has no flaws. I cannot imagine why any reviewer would give it less than five stars. If you are a serious student of Spanish, or just an English speaker with a familiarity with Spanish who wants to know his own tongue better, this is the book for you.