What do you call #?

Try it. Phone an American and they will tell you to “press the pound key.” Phone a Briton and it is the hash key. A copy-editor calls it the number sign; a programmer calls it a hash and uses it to start a comment; a musician glances at it and reads sharp; a teenager calls it a hashtag and cannot imagine it meaning anything else. And a small band of pedants, delighted with themselves, call it the octothorpe.

They are all describing the same twenty-three-year-old key on a telephone and the same character on your keyboard — a character whose official Unicode name, for the record, is the flat and unhelpful number sign (U+0023). How did one little grid of lines collect so many names? The answer runs from a Roman weighing-scale to a Bell Labs patent to a single tweet in 2007, and it is a small masterclass in how words actually behave.

It started as a pound — of weight

Begin with the oldest name, and the strangest: the pound sign. Not the British currency — that is £, a different mark entirely — but the weight. For most of its life, long before telephones, # meant “pounds,” the way we still write 5# on a sack of flour to mean five pounds heavy.

Why “pound”? The most repeated story — and it should be said up front that there is no hard proof for it — traces the shape back to a hurried abbreviation for the Latin libra pondo, “a pound by weight.” Clerks shortened it to lb and sometimes wrote it as ℔ — an lb with a bar drawn across the ascenders to mark it as an abbreviation. Scrawled fast, again and again, the looping letters are said to have collapsed into a tidy little lattice: #. Whether that is literally what happened, nobody can prove; rival accounts tie the sign to telegraph codes instead. But the name is not in doubt, and it is a quiet marvel.

That single Latin word, libra, is still weighing things all over your life. It is the lb on the bathroom scale. It is the L dressed up with a crossbar in the British pound, £. It is the constellation and star-sign Libra, the Scales. And pondo, “by weight,” is simply the English word pound wearing a toga.

So before # was anything modern, it was a fossil of commerce — a shorthand for heaviness that most of its users could not have unpacked if you asked them. They just knew what it meant, because they had met it on a thousand invoices. Hold that thought.

The key that needed a name

The symbol might have lived out its days quietly on grocers’ scales if not for the telephone. When Bell Labs engineers designed the push-button touch-tone keypad in the 1960s, a twelve-key grid left two corners spare below the digits. They filled them with the asterisk, *, and our friend # — two characters already sitting on a typewriter, handy for the coming age of menus and codes.

And here a genuinely odd thing happened: the symbol got a brand-new, invented name. Somewhere inside Bell Labs around 1970, someone decided the key deserved a word of its own, and coined octothorpe. The octo- part everyone agrees on — it marks the eight points that stick out around the symbol’s edge. The -thorpe is a glorious mystery. The character first shows up in print in a Bell Labs patent filed in 1973, but the back-story was never written down, so the engineers’ later memories don’t match.

One of them, Don Macpherson, is said to have wanted an unmistakable word for training manuals and to have built it as a half-tribute to the Olympian Jim Thorpe. Another account has a colleague inventing the deliberately silly octotherp just to have something to say. Reference books now hedge: Merriam-Webster lists the word (and notes it is also spelled octothorp), while flagging the whole origin as uncertain. It is one of the rare English words we can watch being born inside a corporation — and still cannot fully explain.

The tweet that changed everything

For decades, then, # sat in its corner: pounds for the Americans, numbers for the editors, hash for the British and the programmers. Then, on 23 August 2007, a designer named Chris Messina walked an idea into Twitter and, when the staff shrugged, simply posted it himself:

“how do you feel about using # (pound) for groups. As in #barcamp [msg]?”

The notion was humble — a way to let a word gather the messages that shared it — and the company reportedly brushed it off as too nerdy to catch on. Messina has always been generous about the credit, pointing out that the # already prefixed channels in the older chat system IRC; he merely carried the habit onto Twitter. But carry it he did, and the hashtag — # plus a word, no spaces — became one of the defining gestures of the next twenty years.

The name followed the fame. In January 2013 the American Dialect Society voted hashtag its Word of the Year for 2012, beating out YOLO and fiscal cliff. A symbol that had meant “pounds of flour” for centuries now meant “search for this, join this, say this with a wink,” and a whole generation learned the second meaning without ever suspecting the first.

One sign, five meanings, zero rules

Line the names up and look at what # actually is: pounds after a number (5#), number before one (#5), sharp to a musician, a comment to a programmer, a tag to everyone with a phone. Same four strokes; five different jobs. Nothing about the shape tells you which one is meant. You know only because you know the situation — the sack of flour, the hotel-room door, the sheet of music, the line of code, the tweet.

That is not a quirk of one odd symbol. It is exactly how most words work. Pound itself is a weight, a currency, an animal enclosure, and the thing you do to a drum. Hash is a symbol, a diced breakfast, a mess (“made a hash of it”), and, to a programmer, a way of scrambling data. A word almost never carries one tidy meaning; it carries a fan of them, and the right one is chosen by the company it keeps.

You learned “hashtag” the right way

Here is the part worth keeping. Nobody sat you down and defined hashtag for you. No teacher drew # on a board and made you recite “a metadata tag prefixed by the number sign.” You met it in the wild — on a screen, inside real sentences, beside real jokes — a hundred times, until its meaning, its tone and even its faint whiff of trying-too-hard were simply yours. You learned a brand-new word, effortlessly, the way children learn their first thousand: by repeated encounter in context, not by definition.

Where vocabla fits

The humble # is a tiny parable of the thing vocabla is built around. A sign, like a word, does not hand you a single fact to memorise; it hands you a range of meanings, and the only way to know which one is in play is to read the room — the context, the company it keeps, the situation it sits in. A translation pair (“# = hashtag”) would have told you almost nothing; it would have hidden the pound, the number, the sharp, the comment.

So vocabla shows you words the way you met hashtag — inside real sentences, where the context quietly teaches you which meaning is live and how the word actually behaves. Meet a word enough times in that living company and you don’t end up with a definition you can recite. You end up with something far better: a word you simply know how to use, the way you know, without thinking, exactly what # means the instant you see where it is standing.

Pound, hash, number, sharp, octothorpe, hashtag. Six names, one little lattice of lines — and you sort them all, instantly, without a single rule. That is not a party trick. That is what fluency feels like from the inside.