The individual letters of our alphabet can serve many purposes beyond the formation of words. But few, if any, lead as many lives as “X.” While some letters are happy to sit on the page making up sounds, “X” moonlights in all manner of roles, whether it be as a mathematical mystery, a chromosome, or a kiss. Here we look at some of the many jobs that “X” has taken on, and the stories behind each. 

Every math student eventually has to “solve for x,” but the origin of that convention isn’t entirely clear. One popular theory claims it traces back to the Arabic word šay’ or al-shay, meaning “the unknown thing.” When translated into Spanish — a language with no equivalent to the Arabic word — it was replaced by the letter “X,” which had a similar sound. It’s a compelling story, but historians have found no solid evidence to support it. A perhaps more credible explanation points to René Descartes, who in his 1637 work La Géométrie used letters from the end of the alphabet — “X,” “Y,” and “Z” — for unknown quantities, while reserving letters from the beginning for known ones. Either way, “X” became the standard symbol for the unknown in algebra. 

“X” eventually found its way into the wider world of science. In 1891, the cytologist Hermann Henking discovered the X chromosome, but he didn’t understand its function. In keeping with the same “unknown” tradition found in algebra, he simply labeled it “X,” and it was never renamed. Similarly, in 1895, when German physicist Wilhelm Röntgen discovered a form of radiation that could pass through solid objects, he called it X-radiation, again borrowing from the mathematical convention. 

The “X” of the algebraic unknown also made its way into sociology and popular culture. The moniker Generation X arose in the 1950s, referring in general to a generation whose future was yet undetermined. It was later popularized by author Douglas Coupland in his 1991 novel Generation X: Tales for an Accelerated Culture to refer to people born in the 1960s and 1970s. The name describes a generation that felt lost, undefined, and hard to categorize, with the “X” chosen to represent an unknown, unnamed, or resistant identity. 

Apart from representing an entire generation, “X” also came to prominence with one of the most popular TV series of the 1990s: The X-Files, in which Special Agents Fox Mulder and Dana Scully go down a paranormal rabbit hole into the unknown. 

We know that “X” refers to the unknown in algebra, but it also shows up elsewhere in mathematics. The “X” in multiplication equations such as 3 x 4 isn’t technically the same character as the letter — it’s a separate symbol called a saltire. It should really be written as 3 × 4 — with the × raised above the line — rather than 3 x 4, but the latter has become entirely acceptable. Historically, the saltire symbol was a common symbol in heraldry called the St. Andrew’s Cross; it appears, for example, on the flag of Scotland. Historians believe the saltire was introduced as a symbol for multiplication by the English mathematician William Oughtred in the early 17th century, and was widely popularized following the publication of his 1631 textbook Clavis Mathematicae. 

The idea of pirates marking treasure maps with an “X” is basically a myth. While “X” may have been used to mark locations on maps — it is, after all, a simple, logical, and easily recognizable symbol for marking a specific point — the concept of “‘X’ marks the spot” has more to do with fiction than reality. Robert Louis Stevenson’s 1883 adventure novel Treasure Island helped popularize the idea, although it never once mentions the letter “X” marking anything — it instead mentions “three red crosses” on a map. But such was the popularity of Treasure Island and the many adaptations that followed that it nonetheless helped establish the widespread notion of using “X” to mark an important spot — particularly buried treasure — on maps. 

The practice of signing off a note with an “X” to represent a kiss is old enough that its exact origin is debated, but one common explanation ties it back to an age when illiteracy was widespread. In the Middle Ages, people who couldn’t write their own name signed documents with an “X” instead, and some would kiss the mark as a show of sincerity (similar to swearing on a Bible). Examples of using an “X” or a string of “X’s” as a blessing are found in letters from the 18th century. According to the Oxford English Dictionary, the first clear example of “X” to mean a kiss comes from an 1878 novel by Florence Montgomery: “This letter..ends with the inevitable row of kisses,—sometimes expressed by X X X X X, and sometimes by O O O O O, according to the taste of the young scribbler” — strikingly similar to the XOXO still used today. 

“Xmas” isn’t some modern abbreviation that strips the “Christ” out of Christmas. The “X” actually represents the Greek letter chi, which is the first letter in Christos — the Greek word for Christ. Christian scribes have been using the chi symbol as an entirely acceptable shorthand for “Christ” for centuries — meaning that “Xmas” has a much older and more religious pedigree than its casual modern usage suggests.

If something is referred to as X-rated, it’s likely suitable for adults only and might contain content or scenes of a titillating nature. This comes from movie classifications, beginning when the British Board of Film Classification introduced an X certificate in 1951 for anything unsuitable for viewers under the age of 16. (The BBFC never directly stated why “X” was selected, but it was likely inspired by the “X” in “explicit content.”) The adult film industry soon adopted “X” — and “XXX” — as a badge of explicitness, forcing film boards to rename their classifications (to NC-17, for example). But “X-rated” had already become a common term and still serves as a catchall expression for anything of a particularly naughty nature. 

Texting habits have gotten us used to typing out everything in lowercase letters and even dropping punctuation. But when you’re using standard grammatical rules, the stand-alone “I” gets capitalized — autocorrect may even do this for you when you text. This rule is actually pretty unusual, as English is the only major language that capitalizes its first-person singular pronoun.

Capitalizing proper nouns, such as the names of people and places, is not uncommon in other languages, but English takes it a step further by giving one very ordinary pronoun a distinction that its counterparts elsewhere don’t get. Is it a case of ego-gone-mad? Hardly. In fact, the linguistic quirk happened almost by accident.

The most common theory about how “I” became so important has us going back to Old and Middle English, when the first-person pronoun looked quite different. It was often written as ic but later appeared in a variety of forms, including ich, ic, I, and i. And, importantly, there was nothing particularly special about its capitalization.

Over time, English pronunciation changed, and the “c” disappeared. That left English speakers with an extremely short word: “i.” When you’re writing an entire manuscript by hand, a single lowercase “i” doesn’t exactly command attention. It can be difficult to distinguish on the page, especially when it’s sitting by itself between other words. One theory is that medieval scribes began making the pronoun taller simply to make it easier to see. By the late 1300s, the stand-alone “i” had developed into the taller “I” we recognize today.

This beefed-up “I” grew in popularity throughout the 13th and 14th centuries. A manuscript of Geoffrey Chaucer’s The Canterbury Tales was among the first examples of the shift.

There is, admittedly, something amusing about English being the only major language in which the person speaking gets a capital letter every time they mention themselves. For example, the first-person pronoun is je in French and yo in Spanish. 

Some scholars have proposed that the capitalization could have reflected the grammatical importance of “I,” as the pronoun is frequently the subject of a sentence. Others have suggested that capitalizing “I” gives the writer a visual reminder of their own importance.

It’s a fun theory, but it has an obvious problem.

If English speakers were really capitalizing pronouns to flatter themselves, why stop at “I”? Why not do the same to “me,” “my,” or “mine”? And, while we’re at it, why not capitalize “we” or “us”?

While there are many theories, the real answer may simply be that in the Middle Ages capitalization rules weren’t nearly as standardized as they are today.

For centuries, writers and printers used capital letters inconsistently. Capitals (or majuscules, in printing vernacular) could be used for emphasis, decoration, or simply because that was the convention a particular writer or printer happened to follow. Formal rules regarding capitalization didn’t arrive until much later, in the 1700s.

By the time those rules began to crystallize, the capital “I” had already established itself. There was no particular reason to change it, but there were plenty of practical reasons to keep it.

So while today’s capital “I” can look like a tiny monument to the self, its origins appear to be considerably less narcissistic. English didn’t necessarily decide that “I” was important. It just decided that “i” was too  hard to see.

For a surprisingly long period of history, reciting the alphabet didn’t end where you’d expect it to. Children reading from schoolroom primers didn’t stop at “z.” Instead, they habitually tacked on one more symbol: a curvy character that wasn’t a letter at all, but a shorthand squiggle for the word “and.” That symbol eventually earned its own peculiar name — the ampersand — with an equally peculiar etymology. Here’s why the ampersand once had a place as the alphabet’s unofficial 27th member.

From Roman Shorthand to Schoolroom Standard

The story of the ampersand begins around 2,000 years ago, when it was not a distinct symbol but a ligature — a scribe’s shortcut created by joining the letters “e” and “t” from the Latin word et, meaning “and.” Roman scribes writing in cursive began fusing the two letters together into a single, quick stroke to save time and space. Over centuries of handwriting, the fused et gradually smoothed into the rounded, looping shape recognizable today as the “&” symbol. 

By the time English-language schoolbooks and hornbooks — primers used to teach children their letters — became common in the 18th and 19th centuries, the “&” symbol had become a familiar, everyday piece of written English meaning “and.” It was so common, in fact, that it earned a spot directly after “Z” in many schoolroom recitations of the alphabet, in effect becoming the 27th letter (or quasi-letter, as Merriam-Webster calls it) of the alphabet. 

Rather than finishing an alphabetic recitation by saying “X, Y, Z, and” — which would have been confusing and somewhat abrupt — students were taught to finish the alphabet by saying “X, Y, Z, and per se ‘and.’” Here, “per se” comes from the Latin term meaning “by itself,” so the students were essentially saying, “X, Y, Z, and by itself ‘and.’” 

Why It’s Called “Ampersand”

“Ampersand” is a peculiar-sounding word — a word one might imagine comes from Latin or Greek. But its etymological origins actually lie directly in the alphabetic recitations described above. Recited quickly and repeatedly by generations of schoolchildren, that mouthful of “and per se ‘and’” gradually slurred together into a single word: “And per se ‘and’” became “ampersand.”

The word “ampersand” first appears in written form in the late 18th century. One of the earliest examples comes from Samuel Jackson Pratt’s 1795 travelogue, Gleanings through Wales, Holland, and Westphalia. This example is particularly notable because rather than using the now-common expression “from A to Z,” Pratt wrote, “Having tried all the historians from great A, to ampersand.” 

Falling Out of the Alphabet

Despite its long run as an honorary 27th letter, the ampersand was never actually a true letter of the alphabet. It always represented a whole word rather than a single sound, which set it apart from the rest of the alphabet in a fundamental way. 

Eventually, as formal alphabet instruction evolved and became more standardized, educators dropped the symbol from classroom recitation, treating it instead as a separate punctuation mark and typographical symbol rather than a letter in its own right. By the late 19th century, “&” was no longer part of the English alphabet. 

The ampersand itself, of course, never disappeared. It remains a fixture of logos, legal documents, and company names, and while it lost its place in the alphabet, it’s still doing the same basic job: standing in for the word “and.”

While dog names such as Fido and Rover were once incredibly common, they’re not the most popular among the goldendoodles and dachshunds of today. The American Kennel Club tracks the most common dog names on its rolls, and many of the most widely used dog names now are also frequently used as human names, outside of a few exceptions. Here’s the organization’s list of the top 10 most popular girl and boy dog names from 2025, and a quick look at what each of those names means.

1. Luna
2. Bella
3. Daisy
4. Lucy
5. Ruby
6. Willow
7. Maggie
8. Penny
9. Nova
10. Sadie

Luna — Latin for “the moon.” It’s a common term in other Romance languages as well, such as Spanish and Italian.

Bella — A shortened version of the name Isabella. It’s often associated with the Italian term bella, meaning “beautiful.”

Daisy — Derived from the Old English dægeseage, meaning “day eye.” It refers to white and yellow flowers commonly called daisies.

Lucy — The English form of the name Lucia, or the feminine form of the name Lucius. It comes from the Latin lux, meaning “light.”

Ruby — From the Latin rubeus, meaning “red.” It’s widely used to refer to the red precious stone known as a ruby.

Willow — A name originally coined for willow trees. It comes from the Old English word welig, meaning “willow tree.” 

Maggie — The diminutive form of the name Margaret. It’s derived from the Greek μαργαρίτης (margarites), meaning “pearl.”

Penny — The diminutive form of the name Penelope. It’s derived from the Greek πηνέλοψ (penelope), referring to a type of duck.

Nova — Derived from the Latin term novus, meaning “new.” It’s often used today to refer to celestial objects such as supernovae.

Sadie — The diminutive form of the name Sarah. It comes from the Hebrew שָׂרָה (sara), meaning “lady” or “noblewoman.”

1. Max
2. Hank
3. Teddy
4. Cooper
5. Gus
6. Bear
7. Duke
8. Maverick
9. Charlie
10. Finn

Max — A shortened form of the name Maximilian. It comes from the Latin maximus, meaning “greatest.”

Hank — A shortened version of Hankin, which was once a nickname for the name John in the medieval era. It’s more commonly used as a diminutive for the name Henry today.

Teddy — A nickname for people named Edward (which comes from the Old English ead, meaning “wealth”) or Theodore (from the Greek Theodoros, meaning “gift of god”).

Cooper — Derived from the Middle English “couper.” It was once a common surname for barrel makers, as people in that profession were known as coopers.

Gus — The diminutive form of Augustus (a name meaning “exalted” that comes from the Latin augeo) or Angus (from the Old Irish ÓengusI, which likely means “one strength”).

Bear — Likely derived from the Old English bera, meaning “brown.”

Duke — A term of nobility derived from the Latin dux, meaning “leader.”

Maverick — An English word meaning “independent” that was taken from the surname of a 19th-century Texas rancher who let his cattle roam freely.

Charlie — The diminutive form of Charles, which is the English form of the Latin name Carolus, which itself comes from the Germanic Karl, meaning “man.”

Finn — A name that comes from the Old Irish language, meaning “blessed.”