According to Plato, wonder is at the origin of wisdom: “It is precisely of the philosopher that you feel, that you are full of wonder; philosophizing has no other beginning than this” Platone, Teeteto 155 d.
But it is Aristotle who gives the most complete definition: “In fact, men began to philosophize, now as originally, because of wonder: while at first they were amazed at the simplest difficulties, later, as they progressed little by little, they came to pose more and more problems: for example the problems concerning the phenomena of the moon and those of the sun and the stars, or problems concerning the generation of the entire universe” Aristotele, Metafisica, 982b-983.