Books that have informed my education over the years

I'll take these one at a time, and try to post at least one per week.  Not sure how many total I will include.  

I will try to find the online free version for a link, but may not always be able to.

The first is Greek Philosophical Terms: A Historical Lexicon (editor: Francis E. Peters, 1987).

It's better than a mere dictionary listing terms in that most of the definitions provide literary context in classical sources, from the pre-Socratics through Plato up to Aristotle and a little later (but all pre-Christian).

And, in a way, it's better than a book that expands at length about classical philosophy, because it provides focused, bite-sized chunks of useful information which, as an ancillary, can either illuminate some philosophy text you're reading, or can be experienced as a beginning of your own search, arousing a curiosity that might lead you to pick up Plato or Aristotle for a fuller appreciation.

The first time I saw it, I was impressed that it listed such a recondite term as parenklisis.