I have posted this in the past, but it seemed like a good time of the year to remind everyone about it.
I can't tell you how many times I have heard people complain about Xmas - "Don't take Christ out of Christmas!" In reality, that is not what is happening. Xmas is what is known as a Nomina Sacra, an ancient way of shortening the name of Christ out of respect. Christ is in the "X," the Greek letter Chi, which is the first letter used to spell "Christ" in Greek. It is an abbreviation, one used quite often by early Christians.
Another example is to the right. The early church used the first two Greek letters in the word Christ, chi (C) and rho ( R), a symbol that later became part of the official standard of the emperor Constantine.
Another example is the symbol of the fish, one of the earliest symbols of Christians that has been found on the walls of the catacombs of Rome. It originated from using the first letter of several titles of Jesus (Jesus Christ Son of God Savior). When combined these initial letters together spelled the Greek word for fish
So the next time you see Xmas in a store don't tell them "hey, put Christ back in Christmas." Instead you might thank them for partaking in an ancient Christian tradition of referring to Christ with a Greek letter. I doubt many will know what you are talking about.