The most common Greek word translated as "world" is
κόσμος (kosmos). However, it doesn't have exactly the same connotations as the English "world." While it can refer to the physical universe, it more often carries the meaning of "order," "harmony," "ornament," or even "the civilized world." So, the best translation depends heavily on context.
Other words can also be translated as "world" depending on the nuance:
* γῆ (gē): Refers specifically to the Earth, the land.
* οἰκουμένη (oikoumenē): Means the "inhabited world," the known world of a particular time.
Therefore, simply saying "κόσμος" is the Greek word for "world" is an oversimplification. It's a richer and more nuanced term.