The history of the word “Xmas” is actually more respectable — and fascinating — than you might suspect. First of all, the abbreviation predates by centuries its use in gaudy advertisements. It was first used in the mid 1500s. X is the Greek letter “chi,” the initial letter in the word Χριστός. And here’s the kicker: Χριστός means “Christ.” X has been an acceptable representation of the word “Christ” for hundreds of years. This device is known as a Christogram. The mas in Xmas is the Old English word for “mass.” In the same vein, the dignified terms Xpian and Xtian have been used in place of the word “Christian.”
So there you have it.