Words change over time—their meaning, their usage, and even their spelling. Take Christmas and its shortened version, Xmas, for example. We see Xmas written nearly everywhere, from holiday advertisements to Christmas cards. The word Christmas comes from the combination of the words ‘Christ’ and ‘mass.’ But where did the X in Xmas come from, and what does it mean?
In the Greek alphabet, X is the symbol for the letter ‘chi.’ Chi (or X) is the first letter in the Greek word for Christ. In the early days of the Christian church, Christians used the letter X as a secret symbol to indicate their membership in the church to others.
If you know the Greek meaning of X, Xmas and Christmas essentially mean the same thing: Christ + mas = Christmas.