Diophantus Syllabification: (Di·o·phan·tus)Pronunciation: /ˌdīəˈfantəs/Definition of Diophantus (fl. circa ad 250), Greek mathematician. He was the first to attempt an algebraical notation, showing in Arithmetica how to solve simple and quadratic equations. Diophantus in other Oxford dictionaries Definition of Diophantus in the British & World English dictionary