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 Latin radix (see root (n.)). 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.
22nd letter of the Greek alphabet, representing a -kh- sound (see ch). The letter is shaped like an X, and so the Greek letter name was used figuratively to signify such a shape or arrangement (e.g. khiasma "two things placed crosswise;" khiastos "arranged diagonally; marked with an X;" khiazein "to mark with an 'X', to write the letter 'X'"). Some dialects used chi to represent the -ks- sound properly belonging to xi; Latin picked this up and the sound value of chi in Latin-derived alphabets is now that of English X.
chi or khi (kī)
n.
Symbol χ The 22nd letter of the Greek alphabet.
A variety of amphetamine narcotic: Ecstasy, by emergency order of the Drug Enforcement Administration, illegal (1980s+ Narcotics)
A former wife or husband, girlfriend or boyfriend, etc: He introduced his ex rather casually, considering they were together 27 years (1929+)
A person's signature: Just put your X on this and we're in business
[fr the custom of an illiterate person to make an X in place of a written signature]
Ecstasy, a variety of amphetamine narcotic (1990s+ Narcotics)
verbTo use the narcotic ecstasy: Many of us have had the experience of being around someone who is X-ing
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[Jargon File]
(1999-09-15)
American band whose tales of urban decay, corruption, and sleaze, delivered with skilled musicianship and unique vocal harmonies, marked them as important contributors to the punk movement. The original members were Exene Cervenka (original name Christine Cervenka; b. Feb. 1, 1956, Chicago, Ill., U.S., ), John Doe (b. Feb. 25, 1953, Decatur, Ill., ), Billy Zoom (original name Ty Kindell; b. Feb. 20, 1948, Illinois, ), and D.J. Bonebrake (b. Dec. 8, 1955, North Hollywood, Calif., ). Later members included Dave Alvin (b. Nov. 11, 1955, Los Angeles, Calif., ) and Tony Gilkyson.