This word is beginning to appear in a few dictionaries, but still seems mostly to be a jargon term of the North American telephone business for the handset symbol #. It has reached semi-official status by being mentioned in international standards documents but that’s no guarantee of a wide circulation any time soon.
Octothorpe is just one of a plethora of names for the symbol. In the US it’s often called the pound key, because it has long been used to mark numbers related to weight, or for similar reasons the number sign, which is one of its internationally agreed names. Elsewhere it is commonly called hash, a term dating from the 1970s that may have been a popular misunderstanding of hatch. Many humorous or slangy terms have also been recorded, none of them with wide circulation: tic-tac-toe, gate, crunch, and many others. In 1989, one of the international standards bodies settled on square as the official name, seemingly on the grounds that most languages had an equivalent in its vocabulary, so it could be easily translated. As a result, the British Post Office, then responsible for telecommunications, settled on square and it is still used publicly by its successor organisation, British Telecom (BT).
With all these terms about, inventing a new one, especially such an odd-ball one as octothorpe, would seem to serve no practical purpose. The evidence suggests that it was originally a jokey term among engineers at Bell Labs in the USA. In the early 1960s, the Labs were working on ways to interface telephones to computers and invented what is now called touch-tone dialling. This needed two additional special keys on handsets, both of which have since become standard. One of these is the * symbol, usually known as the asterisk but which Bell Labs decided to call the star key. The other was the # symbol.
The word has appeared in many forms, including octothorn, octalthorp, octothorp, and octatherp as well as octothorpe. There are at least five stories circulating about its source. Nobody is in any doubt about the first part, which is obviously enough from the Latin (or Greek) word for eight, as in octagon for an eight-sided figure, because of the eight points on the symbol. It’s the second half that puzzles the experts.
The American Heritage Dictionary says that it comes from the family name of James Edward Oglethorpe, the eighteenth-century English philanthropist who secured a charter for the colony of Georgia in 1732 as a refuge for debtors. This is very unlikely as Mr Oglethorpe’s name is hardly a household word these days (at least, outside Georgia).
A second story says it’s a whimsical creation based on the idea that the symbol looks like a village surrounded by eight fields. Thorp is the Old Norse word for a village, which appears in many English place names, such as Scunthorpe or Cleethorpes, though it’s not known in North America. This is possible, though perhaps a little stretched.
A third story is documented, since Ralph Carlsen of Bell Laboratories wrote a memorandum about it just before his retirement in 1995. He records that in the early 1960s a Bell Labs engineer, Don Macpherson, went to instruct their first client, the Mayo Clinic, in the use of a new telephone system. He felt the need for a fresh and unambiguous name for the # symbol. He was apparently at that time active in a group that was trying to get the Olympic medals of the athlete Jim Thorpe returned from Sweden, so he decided to add thorpe to the end. (Jim Thorpe, a native American who has been described as the greatest athlete of the twentieth century, had won two medals at the 1912 Olympics in Sweden, but had been disqualified because he was found to have accepted money for playing baseball three years earlier, so making him a professional. His medals were finally returned in 1983.)
In 2006 Douglas A Kerr documented his memories of the genesis of the term. Though the background facts about the development of the telephone system and the need for the new symbols match those of other sources, his story about the creation of the term is quite different. He says that it was a joke term, originally octatherp, invented by two friends, John C Schaak and Herbert T Uthlaut, who deliberately included the th sound that would be difficult for speakers of some languages to say. Mr Kerr says that he and the others quietly introduced it into various documents until it caught on.
Unfortunately, there’s no corroborative evidence for any of these stories. Though those of Carlsen and Kerr are anecdotally rich and circumstantial, they have to be regarded by etymologists with some caution because they aren’t backed up by contemporary evidence. In fact, the first appearance of the word in print isn’t until 1974 and that makes clear that the word was not widely known even then within the Bell telephone system.