This from our local paper letters to the editor - don't know the

...The X in Xmas is the 22nd letter of the greek alphabet.
pronounced "chi," is has been the symbol for "Christ" among christians
since the earliest days of gentile christianity, when the followers
spoke greek. Chi is the first letter of the greek word "Christos" in
english letters, which means "anointed" and is a translation of the
hebrew/aramaic term "messias" or "messiah." It was later translated
into english as "Christ." The term "Xmas" has been used by religious
christians in europe since the 16th century. Carol