Sat·urn \ˈsat-ərn\ Roman mythological character. A god of agriculture in Roman mythology, Saturn taught humans how to till the fields and enjoy the fruits of civilization. His festival was called the Saturnalia and took place in late December. Lasting a week, it was the merriest and most popular of the Roman festivals. The planet Saturn, named after the god, was believed by the ancients to be made of lead.