What's the difference between i.e. and e.g.?
"Christmas," 1551, X'temmas, wherein the X is an abbreviation for Christ in Christmas, from first letter of Greek Christos "Christ" (see Christ). The earlier way to abbreviate it was Xp- or Xr-, corresponding to "Chr-," and the form Xres mæsse for "Christmas" appears in the "Anglo-Saxon Chronicle" (c.1100).