early 14c., philosophre, "scholar, learned person, wise person; one devoted to the search for universal truth, a student of metaphysical and moral sciences," replacing Old English philosophe, from Latin philosophus "philosopher," from Greek philosophos "philosopher, sage, one who speculates on the nature of things and truth," literally "lover of wisdom," from philos "loving" (see philo-) + sophos "wise; a sage" (see sophist). The form with -er is from an Anglo-French or Old French variant of philosophe with an agent-noun ending. Fem. forms were philosophress (1630s), philosophess (1660s).
Pythagoras was the first who called himself philosophos, instead of sophos, 'wise man,' since this latter term was suggestive of immodesty. [Klein]
Philosopher in the Middle Ages also could be "alchemist, magician, diviner," hence Philosophers' stone (late 14c., translating Medieval Latin lapis philosophorum, early 12c.), 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. In French pierre philosophale, in German der Stein der Weisen.