Māius

Maia was an old Italian goddess of growth and increase. Her name comes from the Latin root maius, meaning 'greater' or 'larger' — the same root behind the word 'major.' The Romans associated her with the warming earth and the growing season. Offerings to Maia were made on May 1 and May 15, always by the flamen Volcanalis, the priest of Vulcan, which suggests she was once connected to volcanic soil and its fertility.

The Greeks had their own Maia — one of the Pleiades, daughter of Atlas, mother of Hermes. When Roman religion absorbed Greek mythology, the two Maias merged. The Italian earth goddess and the Greek mountain nymph became one figure, and her son Hermes became Mercury. This merger was common in Roman religion: find a Greek equivalent, stitch them together, move on.

The poet Ovid, writing in the first century CE, tried to untangle the Maias in his poem Fasti. He concluded the month was named for maiores, 'elders,' as a complement to June (iuniores, 'younger ones'). This elder-and-youth theory has supporters, but most scholars still favor the goddess. Ovid was a poet, not an etymologist.

The English proverb 'Ne'er cast a clout till May be out' — do not remove warm clothing until May ends — dates to at least the 1700s. Some argue 'May' here means the hawthorn blossom (also called may), not the month. Either way, May is the hinge month: winter clothes come off, summer clothes go on. The goddess of growth would approve.