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The X symbol. Its history and meaning

El símbolo x.

The most powerful letter in the alphabet, the symbol X has been used in many fields, from algebra to science, astronomy and spirituality. It is often used to represent the unknown, but its meanings can vary depending on the context. Here’s what you need to know about the meaning of the X symbol, along with its origin and history.

The X symbol. Its history and meaning

Now that Twitter is completely changing its logo and corporate image to X, there are many of us who are interested in knowing what X stands for. In fact, Elon Musk is also starting to use the domain he bought from PayPal:

The X symbol has several meanings, representing the unknown, the secret, danger and the end. It can have mystical significance, as well as scientific or linguistic importance. Here are some of the meanings of the symbol, along with its use in various contexts:

Symbol of the mysterious unknown

In general, the symbol X is used to denote something mysterious or unknown, meant to be solved. In algebra, we are often asked to solve for x as a variable or value that is not yet known. In English, it is commonly used to describe something vague, such as Brand X, or to signify a mysterious person, such as Mr. X.

Symbol for the known

Sometimes the X symbol is used to label specific locations or destinations on maps and meeting places, giving rise to the expression the x marks the spot. In fiction, it is commonly found on treasure maps, showing where hidden treasure is buried. It can also be used to mark where parachutists should land or where actors should be on a stage.

In modern uses, the X is considered a universal signature for those who cannot read or write, indicating their identity, or their agreement to a contract or document. Sometimes, it also marks the part where a document should be dated or signed. Today, we use it to indicate an election, either on an exam or a ballot, although the same symbol is used to mark a crime scene in photographs, or blueprints.

X Symbol as Danger and Death

Some associate the X symbol with overlapping femurs or cross-boned skulls signifying danger and death. Although the crossed tibias were first associated with pirates, in the Jolly Roger insignia, they became a widespread warning of danger in the late 19th century.

Later, both the skull and crossbones and the X symbol on an orange background became the standard for labeling noxious and toxic substances throughout Europe. This is probably one of the reasons why the X symbol acquired a macabre relationship with death.

Error and rejection

Most of the time, the X symbol is used for the concept of error and rejection. For example, it is used to indicate an incorrect answer, especially on an exam, as well as a cancellation that requires a retake.

The end of something

In some context, the X symbol signifies an entity whose existence is over, past and gone. In technical usage, the letter X is often a shortened version of a longer prefix, ex, commonly used to describe former relationships, such as ex-husband, ex-friend, ex-band, or ex-CEO. In informal language, some use the letter X to refer to their ex-spouse or girlfriend.

A modern symbol for kissing

In 1763, the X symbol for kiss is mentioned in the Oxford English Dictionary and was used by Winston Churchill in 1894 when he signed a letter. Some theories suggest that the letter itself resembles two people kissing with the symbols > and < coming together as a kiss, creating the X symbol. Today, it is widely used at the end of emails and text messages to signify a kiss.

Before acquiring its mystical meaning, the X was a letter of the primitive alphabet. Later, it was used to represent the unknown and a variety of concepts in mathematics and science.

In alphabetic symbolism

Letra X caligrafía.

The early alphabet appeared when pictograms evolved into symbols representing individual sounds. The X derives from the Phoenician letter samekh, which represented the consonantal sound /s/. After 200 years, between 1000 and 800 BC, the Greeks borrowed the samekh and called it chi or khi (χ), the 22nd letter of the Greek alphabet from which the X developed.

In Roman numerals

Later, the Romans adopted the symbol chi to designate the letter x in their Latin alphabet. The symbol X also appears in Roman numerals, a letter system used to write numbers. Each letter in the system represents a number, and the X stands for 10. When a horizontal line is drawn over the X, it means 10,000.

In mathematics

In algebra, the symbol X is now used to represent an unknown variable, value or quantity. In 1637, René Descartes used x, y, z for unknown variables to correspond to a, b, c used to denote known quantities. Just keep in mind that a variable need not be denoted by the letter x, as it can be any other letter or symbol. Therefore, its use to represent the unknown could have a deeper and earlier origin.

Some speculate that the use of the symbol x in mathematical equations comes from the Arabic word shay-un meaning something or thing indeterminate. In the ancient text Al-Jabr, a manuscript that established the rules of algebra, mathematical variables were referred to as indeterminate things. It appears throughout the text to represent the part of the equation that is not yet identified.

When the manuscript was translated by Spanish scholars, the Arabic word shay-un could not be translated because Spanish does not have the sh sound. So they used the closest sound, which is the Greek ch sound represented by the letter chi (χ). Eventually, these texts were translated into Latin, where the translators simply substituted the Greek chi (χ) for the Latin X.

In science and other fields

Following the symbol’s use in algebra, the x symbol was eventually used to represent the unknown in other circumstances. When physicist Wilhelm Röntgen discovered a new form of radiation in the 1890s, he called it x-rays because he did not fully understand it. In genetics, early researchers named the X chromosome for its unique properties.

In aerospace, the X symbol represents experimental or special research. In fact, each aircraft is recognized by a letter designating its purpose. X-planes have achieved several firsts in aviation, from innovations to breaking altitude and speed barriers. In addition, astronomers have long used X as a name for a hypothetical planet, a comet of unknown orbit, etc.

Throughout history, the symbol X has acquired various interpretations depending on the context in which it is seen.

In Christianity

Símbolo X en la cruz.

In the Greek language, the letter chi (χ) is the first letter of the word Christ (Χριστός) pronounced khristós, meaning the Anointed One. It is believed that Constantine had seen the Greek letter in a vision, which led him to adopt the Christian faith. Although some associate the X symbol with the cross, scholars say the symbol is more identical to the pagan symbol for the sun.

Today, the X symbol is often used as a symbol for the name of Christ. As a graphic device or christogram, it replaces the word Christ in Christmas, which thus becomes Xmas. The other popular example is the Chi-Rho or XP, the first two letters of Christ in Greek superimposed. In 1021, an Anglo-Saxon scribe went so far as to abbreviate the word Christmas as XPmas to save space in writing.

Some people are fond of symbols to represent their faith. However, the X symbol itself predates Christianity, as it was the symbol of luck in ancient Greece. Today, it is still a debate to use the X as a symbol for Christ at Christmas, considering the many negative meanings of the X, such as unknown and error, but some argue that the controversy is just a misunderstanding of language and history.

In African culture

For many African Americans, the history of their surnames was influenced by slavery in the past. In fact, the symbol X is an absence marker for an unknown African surname. During slavery, their owners assigned them names, and some had no surname.

The most influential figure is Malcom X, African-American leader and supporter of black nationalism, who adopted the X surname in 1952. He said it symbolized the unknown African name of his ancestors. It may seem like a bitter reminder of slavery, but it may also be a statement of his African roots.

The X symbol’s sense of mystery has led to its widespread use in nomenclature, from Malcolm X to Generation X to the science fiction television series X-Files and X-Men.

As a demographic group label

The X symbolism was applied to Generation X, the generation born between 1964 and 1981, probably because they were young people whose future was uncertain.

The term Generation X was first coined by Jane Deverson in a 1964 publication, and popularized by Canadian journalist Douglas Coupland in the 1991 novel, Generation X: Tales for an Accelerated Culture. X is said to be used to describe a group of people who did not want to worry about social status, pressure and money.

However, some speculate that X was given the name Gen X because it is the tenth generation since 1776, and in Roman numerals X means 10. It is also the generation that marks the end of the Baby Boom generation.

In pop culture

Logo X-men.

The science fiction television series The X-Files had a cult following in the 1990s as it revolves around paranormal investigations, the existence of extraterrestrial life, conspiracy theories and paranoia about the U.S. government.

In the Marvel comics and the X-Men movie, the superheroes had an x-gene, which gave rise to extra powers. The 1992 American movie Malcolm X chronicles the life of the African-American activist who lost his original name in slavery.

In e-mail and social networks

Today, the X symbol is widely used at the end of letters to indicate a kiss. Sometimes, the capital X signifies a big kiss, although it should not always be considered a sign of a romantic gesture. Some people simply include it in messages to give them a warm tone, so it is common among friends.


With a degree in Psychology and a passion for flamenco guitar and board games, my professional journey has deeply explored the intricate link between human behavior and marketing. Over the years, I've honed my ability to analyze and interpret market trends and consumer responses. At The Color Blog, I blend my psychological insights with my love for writing, providing unique perspectives on marketing, history, and the human interactions that shape our digital age.View Author posts

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