An informal shortening of the phrase "Happy Christmas." The use of X in place of "Christ" comes from the Greek letter chi, the first letter in the Greek spelling of Christ, Χριστός (Christós). Primarily heard in UK, Ireland. Their card reads, "Happy Xmas, from the Nichols Family." Aw, isn't that nice?
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.