The etymology for cornucopia (from Latin) is is cornū “horn” + cōpia “abundance."

The earliest depiction of a cornucopia as a symbol of plenty may be in the Greek myth of Zeus and Amaltheia. In the story, infant Zeus (ancient Greek god of sky and thunder) was left in the care of Amaltheia (either a nymph or she-goat) in a cave on Mount Dikte in Crete. Zeus fed on milk from a goat and when one of her horns broke off, Amaltheia filled it with fresh herbs and fruit in a never-ending supply and gave it to Zeus.

Heracles (Greek)/Hercules (Roman) is also depicted with a cornucopia, but its origins are less clear. Various accounts indicate that he acquired it either by breaking the horn off of the bull Achelous or that it was given to him by another deity.

Several Greek and Roman deities are associated with the cornucopia as a symbol, like Plutus (god of riches,) Demeter (goddess or grain and mother of Plutus,) and Fortuna (goddess of luck.)

It makes sense then that as a commonly known symbol abundance in antiquity, the cornucopia would make its way into modern culture.