What’s the #’s Real Name?

On Twitter, Facebook, and Instagram, you tag your friends with the @ symbol and topics with the #. If you see something that says #WordoftheDay, the tweet or post has something to do with Word of the Day. And once you click on that marked topic, you’ll likely see all public posts about it. It’s a great tool for finding people talking about a particular subject (and for categorizing pictures of your fantastic pet). But what do we call the # symbol? And where did it come from? Some names are common…some not so much.

The # symbol is commonly called the pound sign, number sign, and yes, more recently: the hashtag (but that’s not all).

It’s called the pound sign because the symbol comes from the abbreviation for weight, lb, or “libra pondo” literally “pound by weight” in Latin. When writing lb, it wasn’t uncommon for scribes to cross the letters across the top with a line across the top, like a t (like in these examples).

The phrase number sign arose in Britain because “pound sign” could easily be confused with the British currency. And of course, the # symbol is sometimes spoken as the word “number” as in the word “number two pencil.”

The word hash predates these other terms (but wasn’t very popular until recently). A hash referred to stripes on military jackets as early as 1910, but in the 1980s, people starting using it to refer to the # symbol. Since the ascent of social media and its new prominence in our everyday lives, hashtag has become the favored word for the # symbol.

But the sign’s official name is the octothorpe. What does that mean? It’s actually a made-up word, invented in the same laboratories where the telephone came from. The scientists at Bell Laboratories modified the telephone keypad in the early 1960s and added the # symbol to send instructions to the telephone operating system. Since the # symbol didn’t have a name, the technicians thought one up. They knew it should be called “octo-” something because it has eight ends around the edge. But how to make “octo” into a noun? What happened next is not entirely clear. According to one report, Bell Lab employee Don MacPherson named it after the Olympian Jim Thorpe. Another former employee claims it was a nonsense word, meant as a joke. Another unverifiable report is much more etymologically satisfying: the Old Norse word “thorpe” meant “farm or field”, so octothorpe would literally mean “eight fields.”

Similar symbols appear in many other places. Musicians recognize # as the sharp symbol, denoting a note one half step higher. Copy editors see a symbol meaning “space,” as in “add a space between two sentences.” In computer code, the # symbol means that everything that follows is only comment, not instructions.

Where will the # go next?