December December December is the twelfth and final month of the year in the Julian and Gregorian Calendars and is the seventh and last of seven months to have a length of 31 days. December got its name from the Latin word "decem" (meaning ten) because it was originally the tenth month of the year in the Roman calendar, which began in March. The winter days following December were not included as part of any month. Later, the months of January and February were created out of the monthless period and added to the beginning of the calendar, but December retained
December (Roman month) fixed points of the month: the Nones (5th or 7th), the Ides (13th or 15th), and the Kalends (1st) of the following month. The Nones of December was the 5th, and the Ides the 13th. The last day of December was the "pridie Kalendas Ianuarias," "day before the Januarian Kalends". Roman counting was inclusive; December 9 was "ante diem V Idūs Decembrīs", "the 5th day before the Ides of December," usually abbreviated "a.d. V Id. Dec." (or with the "a.d." omitted altogether); December 24 was "IX Kal. Ian.", "the 9th day before the Kalends of Ianuarius," on the Julian calendar