"Pythagoras was the first who called himself philosophos, instead of sophos, 'wise man,' since this latter term was suggestive of immodesty." [Klein]
Modern form with -r appears early 14c., from an Anglo-Fr. or O.Fr. variant of philosophe, with an agent-noun ending. Philosophy also was used of alchemy in Middle Ages, hence Philosophers' stone (late 14c., translating M.L. lapis philosophorum, c.1130), a reputed solid substance supposed by alchemists to change baser metals into gold or silver; also identified with the elixir and thus given the attribute of prolonging life indefinitely and curing wounds and disease. (Fr. pierre philosophale, Ger. der Stein der Weisen).