The first letter of Χριστός, “Chi,” is written in Greek as X; as an abbreviation, then, the X came to stand in for Jesus Christ in several written forms, including in the “labarum” or the Chi Rho, a military standard used by Constantine the Great that incorporated the first two letters of Christ’s name in Greek: Chi (X) and Rho (p).
Notably, X was also incorporated into what historians say was a telltale sign for early Christians. Writing in the late 19th century, Irish Bishop John Healy noted that “in the early ages of the Church the fish was a very sacred symbol.”
The Greek word for fish, “ἰχθΰς,” was “regarded as a symbol of our Savior himself,” the bishop wrote, “because the letters of the word are the initial letters of the five Greek words signifying Jesus Christ, of God the Son, our savior.”
From this ancient signifier and accompanying tradition, the modern world has the so-called “Jesus Fish,” a popular sign of Christian faith often seen on bumper stickers and front doors.
‘Xmas’ has similarly ancient roots
Given its convenient use as a stand-in for the name of Christ, “X” has, unsurprisingly, been used in connection with Christmas for centuries.
Christophe Rico, a linguist and the dean of the Jerusalem-based Polis Institute, told CNA that “in the Xmas abbreviation, X stands for the Greek letter chi, which is the first letter of Χριστός, ‘Christ’ in Greek.”
Rico said that “since the first centuries of the Christian era,” the chrismon, or Christogram, “associated the chi and the rho Greek letters as a symbol of Christ.”
“So the Xmas abbreviation would just shorten the name of Christ through the first letter of Christ in Greek, pretty much as in the chrismon,” he said.
The earliest known usage of this abbreviation is found in an 11th-century portion of the Anglo-Saxon Chronicle, in which the unknown writer referred to “Xp̄es mæsse uhtan,” or “the morning of Christmas.” Another example can be found in a letter by King Edward VI, who in the 1500s referred to “X’temmas next following.”
