The Greek name commonly used for Pandora’s jar is pithos. A pithos was a large storage vessel, often made of pottery, rather than the small box suggested by the modern English phrase.
The distinction matters because the wording “Pandora’s box” is the result of translation and transmission. In the sixteenth century, Erasmus rendered the Greek vessel with the Latin word pyxis, which means box or small container. That choice helped establish the expression that became familiar in English and many other languages.
A pyxis is itself a different type of object from a pithos. Ancient Greek pottery terms can be confused because both refer to containers, but they describe different forms and uses. The original mythic image is best represented by a large jar, even though “Pandora’s box” remains the standard idiom.