Eratosthenes Syllabification: (Er·a·tos·the·nes)Pronunciation: /ˌerəˈtäsTHəˌnēz/Definition of Eratosthenes (circa 275–194 bc), Greek scholar, geographer, and astronomer. The first systematic geographer of antiquity, he accurately calculated the circumference of the earth. Eratosthenes in other Oxford dictionaries Definition of Eratosthenes in the British & World English dictionary