Why is Christmas abbreviated Xmas?
Dear Straight Dope:
Every December one hears of the need to "put 'Christ' back in Christmas", but never a word about "putting 'X' back in Xmas." So just how did the term "Xmas" come to be used in place of "Christmas"?
Well, that letter may look like an "X" and walk like an "X" and quack like an "X," but it isn't an "X." That's the Greek letter "chi" which is pronounced about like "ch" was in Old English ... which is to say, about how it's pronounced in German today, or in a few imported words, like "Christ" or "Christmas," for example.
"X" (as in chi) was used as an abbreviation for Christ from early times, perhaps initially as a camouflage for the religion. It was the first letter of the word Christos (meaning "the anointed one," e.g., the Messiah) and fortuitously was cross-shaped, so there seemed to be some symbolism or double meaning. It's been used as a scholarly and not-so-scholarly abbreviation since.