Heraclitus Syllabification: (Her·a·cli·tus)Pronunciation: /ˌherəˈklītəs/Definition of Heraclitus (circa 500 bc), Greek philosopher. He believed that fire is the origin of all things and that permanence is an illusion, everything being in a process of constant change. Heraclitus in other Oxford dictionaries Definition of Heraclitus in the British & World English dictionary