"It's the Most Wonderful Time of the Year" goes the festive holiday song.

December is associated with the holidays (Christmas, Hannukah, Kwanzaa) and the end of another year. Yet, few know that the word "December" quite literally means 10th month as its Latin roots "dece-/decem-" refers to the number 10. Now, before you're up in arms crying, "But December is the 12th month, not the 10th", you have to remember that back in ancient Rome, there were only 10 calendar months with the year starting off with March. January and February were eventually added to the calendar, but they were initially added AFTER December, with the year ending in February. Of course, the calendar shifted with the introduction of the Julian calendar (circa 45BCE) and January and February were moved up ahead of March, effectively bumping back the rest of the months by two.  

Before Latin infiltrated the English language, eventually adopting the Latin-based "December" as the official final month of the year, Old English had a different name for this festive month: Gēolmōnað (or Ǣrra Gēola | Ȝēolamōnaþ), which means "yule month". This is where the still-used English words such as "yule" and "yuletide" come from. The word "yule" and "yule month" is a whole different can of worms, so I'll save that for another post, but, in a nutshell, it was a winter celebration. So, while we no longer use "Yule Month" as the official name of December, the association with winter celebrations still stands!