December is the tenth month that closes a twelve-month year — the final and most conspicuous of the four numerical anachronisms that end the Western calendar. Its name means 'tenth,' but it is the twelfth month, and this two-month displacement, shared with September, October, and November, has persisted uncorrected for over 2,100 years. December completes the story of the Roman calendar's evolution from a ten-month agricultural cycle to the global standard of modern timekeeping.
The Latin 'December' derives from 'decem' (ten), with the familiar '-ber' suffix. The numeral 'decem' descends from Proto-Indo-European *déḱm̥ (ten), one of the most securely reconstructed numerals in comparative linguistics: Sanskrit 'dáśa,' Greek 'déka,' Gothic 'taíhun,' Old Irish 'deich,' Welsh 'deg,' Lithuanian 'dešimt,' and English 'ten' (from Proto-Germanic *tehun) all descend from this root. The English words 'decimal,' 'decade,' 'decimate' (originally to kill one in ten), 'dean' (from Latin 'decānus,' leader of ten), and 'dime' (from Latin 'decima,' a tenth) are all siblings of December.
In the calendar of Romulus, December was the tenth and final month — the end of the counted year, after which came an unnamed stretch of winter days before March began the cycle again. When January and February were added, December moved from the final position of a ten-month year to the final position of a twelve-month year, retaining its name but losing its numerical accuracy. The coincidence that it remained the last month — just of a longer year — may explain why there was never any urgency to rename it.
Like November, December was briefly renamed by the emperor Commodus — in this case to 'Amazonius,' after the Amazons, whom Commodus admired as warrior-women and with whom he liked to identify his own gladiatorial persona. His mistress Marcia was sometimes depicted as an Amazon, adding a personal dimension to the renaming. As with all of Commodus's calendar reforms, 'Amazonius' died with the emperor on December 31, 192 CE, and 'December' was immediately restored.
The English word 'December' entered the language in Old English, borrowed directly from Latin. The Anglo-Saxons had two names for this month: 'ǣrra gēola' (before Yule) and 'gēolmōnaþ' (Yule-month), both connecting it to the midwinter festival of Yule — the great pagan Germanic celebration of the winter solstice that was later absorbed into Christmas. The word 'Yule' itself (Old English 'gēol,' Old Norse 'jól') is of uncertain etymology, possibly pre-Germanic.
December's cultural character is dominated by celebration, and this is not a modern invention. The Roman Saturnalia, held from December 17 to 23, was the most anticipated festival of the Roman year — a week of feasting, gift-giving, candle-lighting, gambling, and the temporary inversion of social hierarchies in which slaves were served by their masters and addressed them with impunity. Schools and courts were closed, work was suspended, and the greeting 'Io, Saturnalia!' rang through the
The choice of December 25 as the date of Christmas is itself a calendar history puzzle. No biblical evidence supports this date for Jesus's birth, and the earliest Christians did not celebrate it. The date first appears in a Roman document from 354 CE. The most widely accepted explanation is that December 25 was chosen to coincide with — and eventually replace — the Roman festival of 'Dies Natalis Solis Invicti' (Birthday of the Unconquered Sun), celebrated on the winter solstice as the day when the sun began to return. This solar symbolism
The winter solstice itself, falling around December 21–22, is the astronomical anchor of December's festivities. The shortest day of the year, when the sun reaches its lowest point in the sky before beginning its gradual return, has been celebrated by virtually every Northern Hemisphere culture: the Norse Yule, the Roman Saturnalia, the Iranian Yaldā Night, the Chinese Dongzhi Festival, and countless others. December is, at its core, the month of turning — the darkest point from which the light begins to grow.
December also marks the end of the civil, fiscal, and academic year in many countries, giving it a valedictory character that complements its festive one. The tradition of New Year's Eve celebrations on December 31 — with its countdowns, resolutions, and symbolic fresh starts — brings the calendar full circle, returning to the doorway of Janus that opens January. In this sense, December and January are Janus's two faces made temporal: December looks back at the year that was, and January looks forward to the year that will be.