The use of the colloquial “Xmas” has often been singled out as an example of how this religious celebration has been commercialized and robbed of its religious content. The X in Xmas is actually the descendant of the Greek equivalent of Ch, as in “Christos,” which means “Christ.” The letter X has stood for Christ (look up X in any dictionary) since at least 1100 A.D., and the term “Xmas” was first cited in 1551. The scholarly abbreviation for “Christianity” is actually “Xianity.”
How did Xmas come to stand for Christmas? – Not as modern as you would think
So many people dislike “Xmas” for its supposed crassness that its use is now virtually confined to commercial literature and banners. The New York Times Manual of Style and Usage, for example, offers this simple recommendation for when “Xmas” is acceptable: “Never use.”
So, there you are, Xmas is a lot older than you might think- about 400 years older in fact!