Xmas is an abbreviation for Christmas. It is derived
from the word ΧΡΙΣΤΟΣ, transliterated as Christos, which
is Greek for Christ. Greek is the language in which the
whole New Testament was written.
Originally, Xmas was an abbreviation where the X
represents the Greek letter chi, which is the first
letter of Christ's name. However, because of the modern
interpretations of the letter X, many people are unaware
of this and assume that this abbreviation is meant to
drop Christ from Christmas.