The Oxford Dictionary of Philosophy

A page about a Dictionary!? C'mon! Well, you may not know why you, yes, you not only ought to buy it, but ought to give it to as many good people as you can think of for Christmas. Why? Because it was designed to be interesting and a great browse, and, if you keep your wits about you, humorous. Modesty prevents me from citing some of the things reviewers have said, such as:

This is a marvellous book. Breathtaking in scope and yet rich in detail, it is not only an excellent reference work but a tremendous read. I cannot recommend it highly enough

(Australasian Journal of Philosophy)

Anyhow, here is my overall favourite, top entry:

Elis

City of the Peloponnese in Greece, deserving immortal fame because, in honor of its native son Pyrrho, it passed a law exempting all philosophers from taxation.

And if you want to know who Pyrrho was, your best bet is to buy it