Where Month Names Come From: The Origin of Each Month Name

Twelve names, no obvious pattern: two gods, a festival, an emperor, and four plain numbers that no longer match their positions. The month names origin lies almost entirely in the Roman calendar, and the oddities in the modern list are fossils of decisions made well over two thousand years ago and never tidied up afterwards. Once you know which name came from where, the whole set stops looking arbitrary.

This note walks through all twelve names in order, explains the gods, rites and emperors behind them, and traces how the Latin names displaced the older English ones. If you need the numbers rather than the etymology, the month number reference pairs each name with its position in the year.

What Is the Origin of the Month Names?

All twelve month names are Roman. Four honour gods, one recalls a purification rite, one is disputed, two were renamed for rulers, and four are simply the Latin words for seventh, eighth, ninth and tenth — numbers that fitted a year which used to begin in March.

The earliest Roman calendar had only ten months and ran from Martius to December, leaving the winter roughly uncounted. Tradition credits Numa Pompilius, the second king of Rome, with adding Januarius and Februarius to close the gap. Everything that follows in the modern Gregorian calendar descends from that arrangement, with two later renamings layered on top.

January and February: A God and a Rite

Januarius is named for Janus, the Roman god of doorways, beginnings and transitions, usually shown with two faces looking in opposite directions. A month that looks back at the year ending and forward to the year starting is a neat fit, and it is one of the few month names whose logic still reads clearly.

Februarius takes its name from februa, the purification offerings used in rites held during that part of the year, and from Februa, the festival itself. Because February was the last month of the old Roman year, it also became the month where leftover days were absorbed — the reason it is short, and the reason 29 February was later slotted into it. The consequences of that are traced in how many days in each month.

March to June: Mars, an Opening, and Two Goddesses

The next four names are the oldest layer, from the period when March opened the year. They are also where the evidence gets thinner, because Roman writers already disagreed about two of them.

• Martius: named for Mars, god of war and, earlier, of agriculture. It began the year and the campaigning season, which is why the Roman consular year once started here.
• Aprilis: origin disputed. It is often connected to the Latin aperire, "to open", for buds opening in spring, and sometimes to Aphrodite by way of Etruscan.
• Maius: usually derived from Maia, an early Italic goddess of growth associated with the earth. Ovid also records a rival explanation linking it to the maiores, the elders.
• Junius: most often attributed to Juno, queen of the Roman gods and patron of marriage. The competing ancient reading ties it to the iuniores, the younger men.

That two of the four have contested origins is itself informative: the month names were already ancient when Roman antiquarians tried to explain them, and some of their explanations were guesses. Any account of the month names origin has to live with that uncertainty rather than paper over it, because the evidence for Aprilis in particular does not settle the question either way.

Quintilis and Sextilis: The Months Renamed for Rulers

July and August are the only months named after real people, and both were renamed rather than newly invented. Quintilis, literally "fifth", became Julius in honour of Julius Caesar after his assassination, in recognition of the Julian reform that had put the calendar back in step with the solar year. Sextilis, "sixth", became Augustus for the first emperor, chosen because several of his political and military successes had fallen in that month.

Those two names are the reason the numbered months look wrong today. Quintilis was the fifth month when the year began in March, and it is the seventh now — so the original numbering was already out of step before either renaming happened. The full sequence of shifts is set out in why September is the ninth month.

September to December: The Numbers That Stayed

The last four names are the plainest and the most misleading. September, October, November and December come from the Latin for seven, eight, nine and ten, positions they held in a year that opened with March.

When January and February were added at the front, every one of those months moved two places later without being renamed. The mismatch was never corrected, even during the Julian reform, even during the Gregorian reform of 1582, and even though the two months on either side of them were successfully renamed for emperors. Inertia beat tidiness, and the result is a calendar in which December, the tenth month, is the twelfth. To see how a given month's name and number line up, the this month page shows both for the month in progress.

How Did the Latin Names Reach English?

The Latin month names arrived with Christianity and were reinforced after the Norman Conquest, gradually replacing the Old English month names that had been in ordinary use. The change was slow, taking centuries rather than a single moment.

English therefore has month names twice removed from their sources: Roman gods and rites, filtered through church Latin, then reshaped by Norman French spelling. That layering explains why the modern names look so unlike anything else in the language and why their meanings are invisible to a modern reader. Nothing in the word September announces that it means seventh.

Before that, English had its own set, recorded by the monk Bede in the eighth century: names such as Solmonath for February, Thrimilce for May, Weodmonath for August and Blotmonath for November, drawn from farming, weather and ritual rather than from gods and numbers. They faded as Latin literacy spread through the church and administration, though a handful of their traces survive in Yule for the midwinter months. Other European languages kept their own native systems for far longer, and several still do, which is covered in month names in other languages. Meanwhile the underlying month lengths stayed put, and you can check any of them on the days in month page.

Conclusion

The month names origin is a layered record rather than a system: Janus and the purification rites of Februa at the start, Mars, Maia and Juno in the old opening months, Julius Caesar and Augustus overwriting Quintilis and Sextilis, and four numbered months left stranded two places from where their names say they should be. None of it was planned, and none of it has been fixed, which is why the modern calendar carries the fingerprints of the Roman one so plainly. For the name-to-number mapping in both directions, open the month number page, or start from months.now.