PappusPronunciation: /ˈpapəs/Definition of Pappus (fl. circa 300–350 ad), Greek mathematician; known as Pappus of Alexandria. Little is known of his life, but his Collection of six books (another two are missing) is the principal source of knowledge of the mathematics of his predecessors. Pappus in other Oxford dictionaries Definition of Pappus in the US English dictionary