most English words beginning in -x- are of Greek origin or modern commercial coinages. East Anglian in 14c. showed a tendency to use -x- for initial sh-, sch- (cf. xal for shall), which didn't catch on but seems an improvement over the current system. As a symbol of a kiss on a letter, etc., it is recorded from 1765. In malt liquor, XX denoted "double quality" and XXX "strongest quality" (1827).
Algebraic meaning "unknown quantity" (1660 in English), sometimes said to be from medieval use, originally a crossed -r-, probably from L. radix (see root). Other theories trace it to Arabic, but a more prosaic explanation says Descartes (1637) took x, y, z, the last three letters of the alphabet, for unknowns to correspond to a, b, c, used for known quantities. Used allusively for "unknown person" from 1797, "something unknown" since 1859. As a type of chromosome, attested from 1902 (first so called in German; Henking, 1891). First used 1950 in Britain to designate "films deemed suitable for adults only;" adopted in U.S. Nov. 1, 1968.
1896, translation of Ger. X-strahl, from X, algebraic symbol for an unknown quantity, + Strahl (pl. Strahlen) "beam, ray." Coined 1895 by German scientist Wilhelm Conrad Röntgen (1845-1923), who discovered them.
Mongol city founded by Kublai Khan, 1620s, anglicized form of Shang-tu. Sense of "dream place of magnificence and luxury" derives from Coleridge's poem (1816).
late 16c., spouse of Socrates (5c. B.C.E.), the prototype of the quarrelsome, nagging wife. The name is related to the masc. proper name Xanthippos, a compound of xanthos "yellow" (see xanthous) + hippos "horse" (see equine).
1829, from Gk. xanthos "yellow," of unknown origin. Prefix form xantho- is used in many scientific words; cf. xanthein (1857) "soluble yellow coloring matter in flowers," Huxley's Xanthochroi (1867) "blond, light-skinned races of Europe" (with okhros "pale"), xanthophyll (1838) "yellow coloring matter in autumn leaves."
"small three-masted vessel," by 1745, from Fr. chébec, from It. sciabecco, ultimately from Arabic shabbak "a small warship." Altered by influence of cognate Sp. xabeque, which shows the old way of representing the Spanish sound now spelled -j-.
city in Ohio, from Gk. xenia "hospitality," lit. "state of a guest," from xenos "guest" (see guest). Founded 1803 and named by vote of a town meeting, on suggestion of the Rev. Robert Armstrong to suggest freindliness and hospitality.
gaseous element, 1898, from Gk. xenon, neuter of xenos "foreign, strange" (see guest); coined by its co-discoverer, Scottish chemist Sir William Ramsay (1852-1916); cf. krypton.
1952, trademark taken out by Haloid Co. of Rochester, N.Y., for a copying device, from earlier xerography "photographic reduplication without liquid developers" (1948), from Gk. xeros "dry" (see xerasia) + -ography as in photography. The verb is first attested 1965, from the noun, despite strenuous objection from the Xerox copyright department. Related: Xeroxed; Xeroxing.
king of Persia who reigned 486-465 B.C.E., Gk. Xerxes, from O.Pers. Xšayaršan, lit. "male (i.e. 'hero') among kings," from Xšaya- "to rule over" (cf. shah) + aršan "male, man, hero." The Hebrew rendition was Ahashwerosh, Ahashresh.
"Christmas," 1551, X'temmas, wherein the X is an abbreviation for Christ in Christmas, from first letter of Gk. 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).