Undecimber vs. December — What's the Difference?

Undecimber or Undecember is a name for a thirteenth month in a calendar that normally has twelve months. Duodecimber or Duodecember is similarly a fourteenth month.

December is the twelfth and the last month of the year in the Julian and Gregorian calendars. It is also the last of seven months to have a length of 31 days.

The 12th month of the year in the Gregorian calendar. See Table at calendar.

The twelfth and last month of the year, containing thirty-one days. During this month occurs the winter solstice.

Fig.: With reference to the end of the year and to the winter season; as, the December of his life.

The last (12th) month of the year