What is the X in X-mas?
Old English cros (mid-10c.), from Old Irish cros, probably via Scandinavian, from Latin crux (accusative crucem, genitive crucis) "stake, cross" on which criminals were impaled or hanged, hence, figuratively, "torture, trouble, misery;" originally a tall, round pole; possibly of Phoenician origin. Replaced Old English rood. Also from Latin crux are Italian croce, French croix, Spanish and Portuguese cruz, Dutch kruis, German Kreuz.
"ill-tempered," 1630s, probably from 16c. sense of "contrary, athwart," especially with reference to winds and sailing ships, from cross (n.). Cross-purposes "contradictory intentions" is from 1660s.
c.1200, "make the sign of a cross," from cross (n.). Sense of "to go across" is from c.1400; that of "to cancel by drawing lines over" is from mid-15c. Related: Crossed; crossing.
in the New Testament the instrument of crucifixion, and hence used for the crucifixion of Christ itself (Eph. 2:16; Heb. 12:2; 1 Cor. 1:17, 18; Gal. 5:11; 6:12, 14; Phil. 3:18). The word is also used to denote any severe affliction or trial (Matt. 10:38; 16:24; Mark 8:34; 10:21). The forms in which the cross is represented are these: 1. The crux simplex (I), a "single piece without transom." 2. The crux decussata (X), or St. Andrew's cross. 3. The crux commissa (T), or St. Anthony's cross. 4. The crux immissa (t), or Latin cross, which was the kind of cross on which our Saviour died. Above our Lord's head, on the projecting beam, was placed the "title." (See CRUCIFIXION.) After the conversion, so-called, of Constantine the Great (B.C. 313), the cross first came into use as an emblem of Christianity. He pretended at a critical moment that he saw a flaming cross in the heavens bearing the inscription, "In hoc signo vinces", i.e., By this sign thou shalt conquer, and that on the following night Christ himself appeared and ordered him to take for his standard the sign of this cross. In this form a new standard, called the Labarum, was accordingly made, and borne by the Roman armies. It remained the standard of the Roman army till the downfall of the Western empire. It bore the embroidered monogram of Christ, i.e., the first two Greek letters of his name, X and P (chi and rho), with the Alpha and Omega. (See A.)