philosopher

from 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 -phile) + sophos "wise, a sage" (see sophist). Modern form with -r appears early 14c., from an Anglo-French or Old French variant of philosophe, with an agent-noun ending.

Pythagoras was the first who called himself philosophos, instead of sophos, 'wise man,' since this latter term was suggestive of immodesty. [Klein]

Philosophy also was used of alchemy in Middle Ages, 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. (French pierre philosophale, German der Stein der Weisen).

Someone who engages in philosophy. Some examples of philosophers are Aristotle, Immanuel Kant, and Plato.