I'm curious how the abbreviation into "Xmas" came about, now. Surely, the average person doesn't speak much Greek. Is it an old abbreviation then?
I don't know, might be hypocritical of me since in high school everyone shortened physics and philosophy to φsics and φlo (or sometimes just φ and context dependent) and I never found that weird. I guess the alphabet seems more common knowledge to me than the word for "Christ".