The Greek word commonly translated in this context is pithos.
A pithos was a large ceramic storage jar, and Hesiod uses that kind of vessel in the Pandora story. The word does not mean a small hinged box. It refers to a substantial container used in the ancient Greek world for storing agricultural goods and other supplies.
The “box” wording arose through later translation history. In the sixteenth century, Erasmus rendered the Greek term into Latin as pyxis, a word associated with a box or small container. That choice strongly influenced the form of the story that became standard in European languages.
The translation shift is a classic example of how a myth can change through transmission. The plot remains recognizable, but the object’s shape changes from a large storage jar to a box. “Pandora’s box” is now the established idiom, even though pithos is the more historically precise term for Hesiod’s vessel.