Where does the 'X' for xmas come from?

The response by uath13 was close. In the Koine (common) Greek Christ is spelled Xristos. In Greek, X is the letter Chi (pronounced kye). Useage of Xmas [emp] might have [/emp] started with Christians of our time. modeled after the old Xithus (which I forget now what that means--something to do with deity of Christ). The Assemblies of God have a division to reach out to college students called Chi-Alpha and looks like XA. I beleive they were shooting for Christ's Ambassadors and, in reaching out to college folk that are familiar with soroities and fraternities, they used XA. Getting back to the usage of Xmas, sad to say the world has latched on that in some cases to omit Christ (as noted by comment 3).

this is an effort for people to take Jesus Christ out of Christmas...Sadly, people still use this "phrase" when they are writing about Christmas, or when referring to Christmas in pictures or other forms of media...it was used for the same reason that some people have started to say HAPPY HOLIDAYS instead of MERRY CHRISTMAS...people are scared they are going to offend someone by mentioning the name of Jesus...

It was the roman symbol for Christ.