I think this book may hold the record for most quickly becoming indispensible to me. It contains concise, single paragraph histories of the backgrounds of 8,000 words in our language. One thing I really enjoy about it is the way it combines presentations of the most common, everyday words with the coolest, most interesting ones.
Offhand, one of my favorite words would have to be the word "guitar." Did you know that the word guitar started out as the Greek word "kithara," and came to English by means of two separate routes? On the one hand, it passed directly through Europe, by way of the Roman Empire, becoming "cithara" in Latin and then "citole" in Middle English. On the other hand, it went through North Africa with the Muslims as a "qitar" in Arabic, then into Spanish by way of the Moors as "guitarra," then into French as "guitare," then finally into English as "guitar." (A citole, by the way, for all you non-Chaucer fans out there, was a medieval stringed instrument that we no longer have with us.)
That's just one word. There are 7,999 more entries like that, and all of them are amazing. This book is so worth the money it isn't even funny. Two million thumbs up.