Nicomachean Ethics

...[withdr]aw [it], believe me, and let us separate ourselves from our bodies—that is, let us grow accustomed to dying. This, even while we are on earth, will be similar to that celestial life; and when we are carried thither, released from these bonds, the course of our souls will be less delayed. Thus, therefore, we have four definitions of philosophy from Plato himself: two on the part of the subject about which it is concerned, and two on the part of the end for the sake of which it exists. The fifth definition, which also seems to be taken from the part of the end, is that of Pythagoras himself, who called wisdom by the name of philosophy—that is, the love of wisdom. He was the first of all philosophers to begin calling those who were previously called "wise men" "philosophers." For they relate that he once came to Phlius, and there learnedly and copiously discussed certain matters with Leon, the prince of the Phliasians. When Leon had admired his genius and eloquence, he asked him in what art he most relied. But he replied that he knew no art, but was a philosopher, and he explained with many words and similes who philosophers were—that is, students and lovers of wisdom. Since, therefore, according to this opinion, philosophy is a habit by which we know not only those things that are—in the contemplation and knowledge of which wisdom is said to consist—but also God himself, the author of the universe and the cause of all wisdom, as the most noble and most perfect of all, and as the ultimate end most to be desired, as far as it is possible, and are most vehemently drawn to love him; philosophy is deservedly defined by Pythagoras by such a name, that is, the love of wisdom. For as the art of warfare produces victory, or as medicine produces health, so philosophy seems to effect such a love. And this opinion seems to agree with that of Plato, in which he wished the wise to be imitators (as far as is possible for men) and lovers of God. Aristotle brought a sixth definition from the order and rank which philosophy

Philosophy, the love of wisdom.

Leon, prince of the Phliasians.
Pythagoras first called himself a Philosopher.