Gen Xers in the United States grew up calling it a pound sign. Gen Z has always known it as a hashtag. The symbol that can be a shortcut for “number,” make a note sharp in music, and looks like a Tic-Tac-Toe board has multiple names and uses. It also has a surprising origin story that starts with the Ancient Romans.

As language expert and content creator RobWords explains, the # symbol comes from an abbreviation of the word “libra,” which the Romans used for a pound of weight. Libra is what gave us the abbreviation for our own pound measurement (lb) as well as the currency symbol for the British pound (£).

Fast-forward a bit to the time of the printing press, when it became a habit to put a line through the “lb,” signifying that it was an abbreviation. (So something akin to lb.) And that’s where a certain famous scientist influenced history in a non-scientific way.

How Sir Isaac Newton helped create the modern # sign

Writing “lb” by hand, scribes would often draw a line above the letters to indicate it was an abbreviation, sometimes elegantly connecting the rounded part of the “b” to the line above in one fluid movement. But not everyone wrote so neatly. When Newton scribbled it out,........

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