The origin of the
X as a substitute for
Christ in
Xtian,
Xtianity, and, naturally,
Xmas, is something of a mystery -- it might indeed have been intended by non-Christians in a derogatory sense, but it just might, as well, have been a Christian connivance. One perhaps intended simply to
abbreviate, or perhaps complexly to
obfuscate. The X is after all something like a leaned-over
t in its resemblance to that most deathly of reminders, the
cross. In some fonts (and in the
multiplication sign) the lines are in fact
perpendicular. And, even more interestingly, in ancient times,
Jesus Christ was sometimes abbreviated by Christians familiar with the
Greek alphabet with a symbol combining the letters "
Chi" and "
Rho" -- roughly represented in the
Latin alphabet by X and P, respectively. It is very easy to see how those earnestly and noninsultingly referencing Jesus might have whittled their representation down to the point where
X marks the spot.
But then again, if X means Christ, doesn't that mean our
X chromosome is the Christ chromosome, the
X-Acto knife is the Christ-Acto knife, and the
X-men are really the Christ-men?
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Further reading:
"Signs of Xmas" in
Changing Signs of Truth: A Christian Introduction to the Semiotics of Communication, by Crystal L. Downing, pages 89-90.