What is X? It’s a letter, a sound, a word, a symbol — the unknown. It can be sleek and edgy or religious. For such a simple shape of two crossed lines, X carries many meanings. “I might say that it has the most vibes,” says linguist Danny Bate, author of Why Q Needs U. “The most diverse range of vibes.” For this Word of the Week, we strip things down and get xtreme with X.
Thanx to the Greeks
X goes back to Greek around 800 B.C. In one dialect it stood for a kʰ sound (like Scots “loch”); in another it represented two sounds together: ks. That ks version passed to the Romans and into Latin, the ancestor of the English alphabet. In Latin and English, ks can appear at the end of a syllable but not the beginning, so very few native English words start with X. Words that do — xylophone, xenophobia — come from Greek.
Because X stands for two sounds and rarely begins words, it feels like an oddball and carries a bit of mysticism, Bate says. It appears in Old, Middle and modern English but often “has to fight to be used” since other letters can render the same sound (for example, cs). Benjamin Franklin even proposed dropping X from his phonetic alphabet as redundant. Douglas Harper, founder of Etymonline.com, notes that because X “doesn’t fit the way the other letters do,” it’s available for other uses.
X as old symbol
Beyond being a letter, X is a powerful, simple image. Harper points out it’s why people use an X to sign when they can’t write a name, and why X markings once indicated the strength or quality of goods on barrels. The symbol works in literate and illiterate contexts because of its striking look.
X’s role as the Roman numeral for 10 likely grew from tally marks: straight lines for units and crossed diagonally at ten to form an X. Though Roman numerals resemble letters, that’s mostly coincidental. The Romans also associated X with a grim story: St. Andrew was said to have been crucified on an X-shaped cross.
X also abbreviates Christ — the Greek Χ (chi) begins Χριστός (Christós) — so Xmas and Xtian are longstanding shortenings going back centuries.
You’re X’d
X’s mystique deepened in algebra. René Descartes popularized using a, b, c for known quantities and x, y, z for unknowns. After that, x became the universal symbol for an unknown variable and a general shorthand for anything unnamed. By the 19th century, it was common shorthand for any unknown thing. U.S. military records once labeled files about unidentified WWII remains as “X-files.”
That aura of the unknown lent X cultural cool. In late-1970s Los Angeles, a punk band chose the single-letter name X. Singer Exene Cervenka said she liked the idea of not being The Something-or-Other — just a big black X on a marquee. The name carries swagger few other letters could match.
Bate cites The X Factor as another use: the “X factor” denotes some special, unnameable quality. X can also signal independence and resistance. Early 1980s Washington, D.C. straight edge punks drew Xs on their hands to reject drugs and alcohol. By the 1940s, X was already used as a verb meaning to cross out with an X: “You’re X’d — get out of my life,” sang D.C. band The Faith in 1982.
Capitalism comes for X
X’s visual distinctiveness and rarity in English made it useful commercially. Advertisers add X to the end of words to make them pop on the page — think Kleenex, Terminix, Xerox. The Latin prefix ex- (out of, from; later ‘completely’ or ‘without’) also colors X’s associations.
When the Motion Picture Association of America created ratings in the 1960s, the pornography industry adopted the X category and amplified it: XX, XXX became marketing shorthand for extreme sexual content.
More recently, tech and business use X as shorthand in ways like UX and CX for user experience and customer experience, using X instead of E for “experience.”
There are, of course, X-numbered other associations. “X feels like it wants to break out. It wants to be a star somehow,” Harper says. “It’s not allowed to start any words in English except exotic ones. But it’s fighting to be seen somehow. You got to root for X.”
