I always wondered where the X in "Xmas" came from. Or rather, I thought I knew: I thought it symbolized a cross. But recently it occurred to me that the similarity in sound between the words "cross" and "Christ" is an accident; "crossmas" doesn't really make any sense. So why the X?
Maybe I was the only one who didn't know this, but it turns out the X didn't start out as an X at all; it was the Greek letter chi, which is the first letter of the Greek word for Christ.
(Note that "Christ" wasn't some kind of surname for Jesus; it's a title, "the Christ," which derives from the Greek for Messiah, which means "anointed one." Which is why Jewish people often refer to Jesus as "Jesus" rather than "Christ"—"Jesus" being a name rather than a title. Meanwhile, due to a prediction in the book of Isaiah, Jesus is also sometimes known as Immanuel, meaning "God is with us." In the King James Version of the Bible, the relevant line goes "...and shall call his name Immanuel," which always makes me think of the White Knight's distinctions in Through the Looking Glass between the name of something, what the thing is called, and what the thing's name is called.)
So writing "Xmas" is kind of like writing "Chmas"; it's an abbreviation. Perhaps it should have an apostrophe in the middle.
Of course, the X-for-Christ abbreviation is also commonly seen in a visual pun based on an acronym: that fish symbol often seen on cars and in ads for Christian businesses. In ancient times, Christians were widely persecuted; to identify themselves to each other in secret, they devised an acronym, I.X.TH.Y.S. (That is, Iota, Chi, Theta, Upsilon, Sigma—IXTHYS is an awkward mix of letters transliterated from Greek with letters that look like Greek letters, but it's no more awkward than the alternative IXOYE, which looks more like the Greek but bears even less relation to the sounds.) The acronym stood for "Iesous Christos Theou Huios Soter," which is to say "Jesus Christ, God's Son, Savior." And it's a real acronym (not just an initialism), because in Greek it spells "ichthys," which means "fish." So the fish became a symbol of Christianity (and not solely due to the "fishers of men" business). (This symbol apparently has nothing to do with eating fish on "meatless" Fridays; that practice may derive from a Medieval belief that fish spontaneously generated rather than being the result of sexual reproduction, which apparently made them not count as meat.)
The IXTHYS/Jesus fish has spawned a host of parodies. The most common, at least in the San Francisco Bay Area, is the Darwin fish-with-legs; I've also seen a "Gefilte" fish (with English lettering designed to look vaguely like Hebrew). Now and then I see a bumper sticker that shows a Jesus fish with jaws open wide, eating a Darwin fish, with the caption "Survival of the fittest." And then there are the really silly variations, like the Satan fish (with pointy ears and tail), the UFO based on the same shape, and the new one I saw this weekend: a Frida fish (with a picture of Frida Kahlo's head stuck onto the front).
I haven't made my own fish yet, but if I did, I would label it either simply "fish" (in generic-food-label letters) or "ghoti."
A final note about the use of "X" as an abbreviation for "Christ": one story has it that Jewish money-lenders in Manhattan at one time were so adamantly anti-Christian that they wouldn't use an X mark for any reason, not even to check off payments. Instead of an X they used a circle—which is to say, in Yiddish, a "kykle." Whence, so the story goes, the derogatory term "kike."
Thanks to Kendra Eshleman, Fran Altvater, and Ed Bernstein for their assistance with this week's column.