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Why is letter X used to symbolize a kiss?

The letter "X" has ambiguous linguistic roots, and has carried various meanings in different contexts. "X" marks the spot of buried treasure on a map, represents a variable in mathematics, or can be used to select a choice on a ballot. Nowadays, it’s also commonly used as a symbol of affection and endearment — especially when it’s paired with "O" to form "XO," signifying kisses and hugs. But how exactly did "X" come to represent a kiss, and when did that originate?

The origins of "X" being associated with a kiss can be traced back to the Middle Ages. In an era when literacy rates were low and formal education was a rare privilege, people who couldn’t write would sign documents with an "X" instead of their name. When people signed with an "X," it wasn't merely a mark; it was a symbol that carried the weight of an oath. To validate their intentions and their "signature," people were also known to kiss the "X." 

How the letter "X" transitioned from a kiss in the name of sincerity to a kiss of romance or affection isn’t clear. The Oxford English Dictionary traces the earliest known use of that meaning to a 1763 letter by British naturalist Gilbert White. In the letter, White signs off, "I am, with many a xxxxxxx and many a Pater noster and Ave Maria, Gil White." This interpretation, however, has been challenged: Stephen Goranson, a researcher at Duke University, instead suggests that the "X" likely represented blessings, not kisses, given its use alongside religious phrases such as "Ave Maria." Indeed, an "X" was historically used as a symbol of the Christian cross. "X" is also the first letter in the Greek word for Christ, Χριστός — hence the well-known abbreviation for Christmas, "Xmas." 

Some linguists suggest an 1894 letter from Winston Churchill to his mother demonstrated a pioneering use of the letter "X" as a symbol for a kiss. The letter reads, “Please excuse bad writing as I am in an awful hurry. (Many kisses.) xxx WSC.” But in additional research, Goranson uncovered other uses of "X" as a symbol for a kiss as early as 1880. An even earlier example dates back to 1878. In Florence Montgomery's novel Seaforth, she describes letters ending with “the inevitable row of kisses; sometimes expressed by x x x x x, and sometimes by o o o o o.” Marcel Danesi, a professor of linguistic anthropology and author of The History of the Kiss!: The Birth of Popular Culture, suggested the association began earlier. He wrote that as the Renaissance era saw an increase of secularism, and with the 18th-century rise of the concept of romantic love, the symbolic "X" gradually expanded beyond its initial utilitarian function to become a gesture of affection.

An easier explanation could simply be the shape of the letter — that it looks like a pair of puckered lips. A linguistic interpretation, meanwhile, might suggest that the use of "X" for a kiss is rooted in its phonetic resemblance to the sound of the word “kiss,” mainly the soft, percussive "ks" sound made when pronouncing "X." The letter is still often written on its own as a sign-off; sometimes a double “XX” will do, and, of course, "X" frequently gets paired with an "O." (Even less is known about the origin of "O" as a symbol for a hug. It’s been suggested that the letter simply looks like a pair of arms wrapped around someone else; as with "X," however, there are other theories as well.)

While the exact reason may never be clear, using an "X" for a personal touch has certainly permeated global communications, and has been perpetuated and reinforced through the rise of digital messaging. Today, the letter "X" is ingrained as a shorthand for affection, and despite its ambiguity, it remains a constant symbol in our ever-evolving language.

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