# cissoid, sistroid

Apparently there was some big sporting event over the weekend, some game played by men with odd-shaped balls. It’s supposed to be macho or something, but the people I’ve talked with about it have focused mainly on the fact that the men were wearing lots of padding and spandex and had a liking for dancing around and patting each other on the buttocks. Now, it happens that a lot of the most likeable guys I know are comfortable with padding and spandex and dancing and so on, but that hardly seems to go with beating other guys to a pulp on a field of grass and mud, which is apparently supposed to be an important component of this game. Guys who like that kind of thing, by my experience, usually call guys who like dancing and padding and so on sissies. So this whole thing is throwing me a bit of a curve.

That might seem like a bad metaphor, since throwing a curve is a baseball reference, and I’m talking here about what Americans and Canadians call football. But when those football players throw their ball, well, that ball has a curve, and brother, that curve is kind of sistroid. And if they say they’re not a bunch of sissy-pants just because they wear spandex and pat each other’s bums, remember that those tight pants of theirs reveal a definite cissoid curve in the butt.

What are cissoid and sistroid curves? They’re really planar geometry, so I’m cheating a bit when I describe 3-D objects with these terms. But the short of it is that a cissoid is the shape formed when two concave curves meet at a point. Consider the bottom of someone’s bottom, and how the lines that describe the lower limit of each cheek meet in the middle. That’s not a classic cissoid (describable in Cartesian terms as y2(2a–x) = x3), but it’s of the general type. Another example would be the line described by a ball bouncing off the ground. A sistroid is the converse: two convex curves meet at a point. Sort of like a cross-section of the tip of a football (an American one), or the nose of a blimp (perhaps one flying over the game to get an aerial view).

But where do these words come from? When we say them, they sound the same except for the /tr/ in the middle of one, but when we spell them, one has ciss where the other has sis. It’s all hissy, but it also makes us think of sissy – also spelled cissy – and sister. What’s the relation?

Well, sister is an old Germanic word. Sissy is just a diminutive formed from sister and in use in its current sense since the later 1800s (and sometimes spelled cissy or cissie since around 1915). Cissoid, on the other hand, comes from Greek κισσός kissos “ivy”, since the curve resembles the tip of an ivy leaf (and here you thought a kiss was always under the mistletoe – well, mistletoe doesn’t even have a cissoid curve). And sistroid comes from Greek σείειν seien “shake” via the noun σείστρον seistron “sistrum” – oh, and a sistrum is a kind of metal shaker made of a frame with rods in it. The sistrums (a.k.a. sistra) I’ve seen haven’t looked sistroid to me, but perhaps when the converse of cissoid was desired they wanted a sister term and that one sounded good.

I suppose I could leap off from that to ask whether, in football, the Ivies are getting their fair shake – the Ivies being the Ivy League schools, not really as focused on sports as some other universities, although the first collegiate football game was played between Harvard (an Ivy) and Tufts (not an Ivy but a similar kind of place). But the truth is that while I am rather uninterested in professional football, I am if anything antipathetic towards what collegiate sport generally is now in the US (much less so in Canada): the tail that wags the dog for a lot of universities (not the Ivies, however). The athletes who are pushed through to fill out their teams aren’t always graded on a curve – other than the curve of the balls they play with.

So I will leave that undiscussed (see paralipsis). We may close instead with a picture of the sissy sisters of spandex and super bowls, their cissoids and sistroids soaring and whistling through the air like asteroids.

Thanks to Michael Corrado for suggesting these words.