A Pocket Philosophical Dictionary, By Voltaire

Not really a dictionary, but a series of short essays on such topics as equality, Hell, miracles, religion, tyranny and superstition by one of the leading spirits of the Enlightenment. The tone is witty, catty, and there are many neat aphorisms such as: "Atheism does not prevent crimes, whereas fanaticism commits them." There are also occasional flashes of an unlovely anti-Semitism, but Voltaire is catholic in his dislikes; the Greeks and Egyptians get it in the neck too. And in his essay on toleration, Voltaire specifically mentions Jews as deserving of tolerance, in an impassioned plea for freedom of belief which is still relevant today.