The Greek word for the large storage jar in Pandora’s story is pithos.
A pithos was a substantial ceramic container used in ancient Greece and the wider Aegean world for storing commodities such as grain, wine, oil, or water. Hesiod used the word pithos when describing the container associated with Pandora. It was not necessarily a small chest or hinged box.
The familiar expression “Pandora’s box” arose through translation history. In the sixteenth century, the humanist Erasmus rendered the Greek term into Latin as pyxis, meaning a box or small container. That wording became influential in later European languages. “Pandora’s jar” is therefore closer to the ancient Greek text, while “Pandora’s box” is the standard modern expression.