“X-K-C-D”, “X.K.C.D.”, or even occasionally “xkcd” is a textual transformation of an incantation associated with Western mysticism, especially certain elements of the Golden Dawn. The abbreviation stands for “X. Kyrie Christi Dominus”, which roughly translates to either “Cross [of] the Lord Christ, [the] Master” or “Christ [the] Lord, Christ [the] Master”, although both translations are grammatically incorrect, and mix both Greek and Latin. The letter X has long been used as an abbreviation for both the name of Christ and for the cross, because of its association with the Greek letter Chi (the first Greek letter of the word “Christ”), and the letter’s superficial resemblance to a crucifix.
The X-K-C-D formula was incorporated into incantations used by members of many Western occult circles, especially those that sought the secrets of “natural magic” (i.e., magic resulting from natural phenomena, and therefore associated with angels and God’s will) rather than “black magic” (magic resulting from the magician’s will, rather than that of God, and traditionally believed to result from consorting and forming pacts with devils and other evil entities).
Ian Sutfield wrote extensively about the proper ritual use of the X-K-C-D formula during his last years in England and during the three years of his exile in Geneva, Switzerland before disappearing, presumably killed. Sutfield generally prescribed that the formula should be repeated three times before the beginning of an incantation, and three times again at the end. Repetition of the X-K-C-D formula was also to occur at intervals throughout the recitation of the incantation, along with the Tetragrammaton (Y-H-W-H) – the name of the God of Israel used by the authors of the Hebrew Bible. The Tetragrammaton was long held to have ritualistic power, and by combining the X-K-C-D formula with it, Sutfield believed it would improve the efficacy of a ritual, because the Father (Y-H-W-H) and the Son (X-K-C-D) were being invoked to interact with the Holy Spirit (which Sutfield believed to be present in the soul of a faithful magician—or any Christian believer—because of the Pentecost), and the presence of the Holy Trinity would bless the magician’s works if the practitioner was humble and worshipful and performing the ritual for righteous purposes.
Randall Munroe is the writer and illustrator of a popular webcomic called “xkcd”, perhaps named ironically since the webcomic’s themes include science, mathematics, technology, and pop culture, and the comic has almost nothing to do with religion or occult occurrences.