## Words No Longer Used

I’ve been listening to the audiobook of At Home by Bill Bryson, and there’s a segment where he talks about words previously used to refer to the bathroom. My favorite is

necessarium

with its Latin meaning of “necessity,” implying that a room dedicated to urinating and defecating may not be something we really want in our house but very much need.

This made me wonder about mathematical words that are no longer in use. Many have gone the way of necessarium, but I think they deserve consideration for reintroduction. Well, maybe not all of them. Let’s have a look…

octothorpe, n. : another name for the pound sign (#); the hashtag. Wouldn’t it be great if #worldoctopusday were read as “octothorpe world octopus day”?

surd, n. : a square root that cannot be reduced further. This word comes from its meaning in phonetics of “mute” or “voiceless” for an unvoiced consonant; in math, it refers to an expression that cannot be expressed (spoken) as a rational number. The following radical would be ab‑surd:

$\sqrt{ab}$

vinculum, n. : a horizontal line drawn over a group of terms in a mathematical expression that serve as a grouping, such as the line on top of a radical that indicates the number for which the root is to be taken, or the fraction bar, which appears over the entire denominator. Still used occasionally, but rarely.

Logo of Vinculum, a global software company.

solidus, n. : the diagonal slash “/” used as the bar between numerator and denominator of an in-line fraction. Also, a famous Roman bodybuilder.
synonym diagonal

virgule, n. : a diagonal slash resembling the solidus, but with slightly less slant, used to denote division for in-line equations. This is also the name for the line used to indicate a choice between two terms in writing, e.g., and/or or pass/fail.

lattermath, n. : aftermath. Okay, not really a math term, but on the list since it contains “math.”

porism, n. : an archaic type of mathematical proposition whose historical purpose is not entirely known. It is used instead of “theorem” by some authors for a small number of results for historical reasons.

Jacob’s staff, n. : a mathematical instrument used for measuring heights and distances; typically, a pole with length markings on it.

anthyphairetic ratio, n. : a continued fraction, such as

$\displaystyle 1 + \frac{2}{3 + \frac{4}{5}}$.

Same number of syllables as parallelogram and inequality, but cooler than either of those. If you looked at anthyphairetic and thought, “that’s Greek to me,” you’d be entirely correct.

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• 1. Xander Henderson  |  October 13, 2020 at 9:50 am

I was taught that a porism is kind of like a corollary, but that it falls out of the proof of a theorem, rather than as a direct result. That is, a corollary is a mathematical proposition which follows immediately from the statement of a theorem, whereas a porism is a result which might be proved in the manner of an earlier theorem, but which is not readily apparent from the statement of that theorem.

In essence a porism is a result that you get after you finish a proof and go “Oh, hey! This same proof gives this other neat result!”

• 2. goldenoj  |  October 13, 2020 at 5:08 pm

Who doesn’t use surd or vinculum?!

• 3. venneblock  |  October 13, 2020 at 10:15 pm

My son said the same thing!

• 4. Gene Thomas  |  October 20, 2020 at 4:52 pm

Here’s another for your list: alligation, which wikipedia explains well. It’s not merely a term no longer used, it’s a body of arithmetical knowledge no longer packaged up separately.

• 5. venneblock  |  October 23, 2020 at 12:31 am

Thanks, Gene. I wasn’t aware of that term, and it was a fascinating read.

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