An informal shortening of the phrase "Merry Christmas." The use of X in place of "Christ" comes from the Greek letter chi, the first letter in the Greek spelling of Christ, ???st?? (Christós). Their card reads, "Merry Xmas, from the Nichols Family." Aw, isn't that nice?
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.