Octothorpe: The Real Name of the # Symbol and the Debate Over Its Origin

A Symbol With Too Many Names

Few punctuation marks have accumulated as many names as #. In the United States, it has been called the number sign (as in #1, meaning number one), the pound sign (on telephone keypads, where it was labeled lb, abbreviated from the Latin libra pondo), and the sharp sign in music notation. In Britain and many Commonwealth countries, it is simply called hash. In programming contexts, it is often called the hash or the octothorpe. And since August 23, 2007, when Twitter developer Chris Messina proposed using it to organize topics in tweets, it has been called the hashtag.

Each name reflects a specific context and use case, and none has fully displaced the others. The octothorpe is the name that carries the most mysterious origin story and generates the most etymological debate, making it the most interesting of the bunch.

Bell Labs and the Telephone Keypad

The name octothorpe appears to have originated in the early 1960s at Bell Telephone Laboratories, when engineers were developing the touch-tone telephone keypad. The standard layout — twelve keys, ten digits plus two symbols — required symbols that callers and operators could refer to by name. The star (*) and the pound/hash (#) symbols needed official designations that would be unambiguous in technical documentation and customer instructions.

Bell Labs engineer Don Macpherson is credited by some accounts with coining "octothorpe" for the # symbol. The "octo" prefix is straightforward: the symbol has eight endpoints (the ends of the four lines that make up the grid-like #). The "thorpe" element is where the disputes begin. Some accounts claim it was named after Jim Thorpe, the Native American Olympic athlete and professional football player, as a tribute. Others suggest "thorpe" was a nonsense syllable invented to pad the word and make it sound official. A third account credits engineer Ralph Carlsen with proposing the name specifically to honor Thorpe.

The Disputed Etymology

What is unusual about the octothorpe origin story is that multiple people who were present at Bell Labs during the relevant period give different accounts. Macpherson, in later interviews, described coining the word himself and naming the second part after Jim Thorpe. Others recall the word being invented collectively in a meeting. Some former Bell Labs employees deny that Thorpe had anything to do with it and describe the "thorpe" element as arbitrary.

The word "octothorpe" first appeared in print in a Bell Labs technical document and was used internally before appearing in any public-facing material. It is possible the true origin is genuinely ambiguous — a word coined collaboratively in a meeting where multiple people later remembered their own contribution most vividly. What is well-established is that the word was coined at Bell Labs in the 1960s specifically to give the # symbol a formal, unambiguous technical name for use in telephony contexts.

How Hashtag Overtook Octothorpe

The rise of "hashtag" as the dominant popular name for # is recent enough to be well-documented. Chris Messina's 2007 proposal to use # for topic grouping in Twitter was not immediately adopted — Twitter's own founders were initially skeptical, thinking it was "too nerdy." The first hashtag used in the way Messina proposed appears to be #barcamp, used to organize conversations about developer conferences. By 2009, Twitter added official support for clickable hashtags, and the concept spread across virtually every social media platform.

"Hashtag" won the popular naming contest because it is descriptive of the new use case — a hash mark used as a tag for categorization — and because millions of people encountered the symbol primarily through social media contexts. The word entered the Oxford English Dictionary in 2014. "Octothorpe" retreated back to technical documentation and linguistic trivia. The symbol itself remained unchanged, carrying all of its names simultaneously, available to mean number, pound, hash, or octothorpe depending entirely on who is using it and why.