What is X? It is a letter, a sound, a symbol and a sign for the unknown. For such a spare mark — two crossed strokes — X wears many meanings: edgy, mystical, religious, commercial. Linguist Danny Bate, author of Why Q Needs U, puts it bluntly: X carries “the most diverse range of vibes.” This is a look at how a simple shape gathered so much baggage.
Its story begins with the Greeks around 800 B.C. In some dialects the symbol stood for a kʰ sound (think the Scottish loch); in others it represented the consonant cluster ks. That ks value passed to the Romans and into Latin, and from there into English. Because the ks sound can occur at the end of a syllable but rarely at the start, few native English words begin with X — most English x‑words, like xylophone or xenophobia, are borrowings from Greek.
That dual-sound quality and its scarcity at word beginnings made X feel like an outsider, a letter with a hint of mysticism. It crept into Old, Middle and modern English but was sometimes skipped because other spellings could do the same job; Benjamin Franklin even proposed dropping X from a phonetic alphabet as redundant. As etymologist Douglas Harper observes, X “doesn’t fit the way the other letters do,” which also left it free to be repurposed.
As an image, X is immediately powerful. Its high contrast makes it useful in both literate and nonliterate contexts: people who couldn’t write signed with an X, merchants marked barrels and goods with Xs to indicate quality or strength, and an X became a handy shorthand to cross things out. The Roman numeral X for ten likely grew from tallying — grouping five or ten marks into a single crossed sign — and the shape also has religious associations: St. Andrew’s cross is said to be X-shaped. In Greek, the letter Chi (Χ) begins the word Christós, so forms like Xmas and Xtian date back centuries as abbreviations.
X’s cultural aura deepened in mathematics. René Descartes popularized using a, b, c for known quantities and x, y, z for the unknowns, and x soon became the default symbol for something unspecified. By the 19th century it was common shorthand for any unknown entity; files about unidentified WWII remains were once labeled “X-files,” a literal bureaucratic echo of that algebraic meaning.
The idea of X as a stand-in for the mysterious or exceptional fed into popular culture. A Los Angeles punk band in the late 1970s chose the single-letter name X; singer Exene Cervenka liked the bluntness of one big black X on a marquee — no need for a longer identity. The phrase “the X factor” likewise signals an ineffable quality. X has also been used as a mark of defiance: early 1980s straight-edge punks in Washington, D.C. drew Xs on their hands to reject drugs and alcohol. By midcentury X had even become a verb — to X someone or something out — captured in the lyric “You’re X’d — get out of my life” from the D.C. band The Faith.
Commercial life seized on X’s visual distinctiveness and rarity. Advertisers tack an X onto brand names to make them pop — Kleenex, Terminix, Xerox — and the Latin prefix ex- (out of, away from, or completely) colors some of those uses. When the Motion Picture Association introduced ratings in the 1960s, X was adopted by the pornography industry and intensified into XX and XXX as shorthand for ever more explicit material. In tech and business, X is now a compact stand-in in acronyms like UX and CX for “user experience” and “customer experience.”
X’s many lives — letter, numeral, symbol, brand, shorthand for the unknown — give it a restless energy. As Harper puts it, X “feels like it wants to break out…It’s not allowed to start any words in English except exotic ones. But it’s fighting to be seen somehow.” That audacity, more than any geometric simplicity, explains why two crossed lines keep turning up everywhere from math textbooks to punk rock flyers.