“The title Republic is a bad translation of the Greek politeia. The Greek word does occur a number of times in the book, as well as forming the title, and in this translation it has invariably been rendered as ‘political system’. Politeia is the public and political life of a community; in Latin this is res publica, ‘public business’; Greek words used to be referred to by their Latin or Latinized titles: hence Republic. The book, however, is not by any stretch of the imagination a treatise on republicanism or Republicanism. Nevertheless, the title is immovable.”
Introduction to Republic, translated by Robin Waterfield. Oxford World Classics.
It is because of information like this that I do prefer Oxford World Classics (OWC) over Penguin Classics. The bibliography, notes and introduction in OWC make them, I think, the best popular series of world literature.