It came from the Old English for "Christ's Mass", Crīstesmæsse, which in turn gave us Cristemasse in Middle English. For all those that like a good "humbug" over the use of Xmas, you should know that using X as an abbreviation for Christ has been around since around 1551, when the word X'temmas was used.
The French word Noël came from Latin (as did most French words) and referred to "birth", or natalis in Latin. Other European languages such as Spanish, Portuguese and Italian all make references to birth as well. Spanish has Navidad, the Portuguese use Natal, and the Italian language gives us Natale.
Now get back to your family and enjoy that turkey!