This is a rather ugly word, but it might make your world sparkle a little more brightly.
You get splines all over the place, though perhaps you've never really noticed them. A spline is basically a sticky-out bit on the edge of a cylinder that makes it act like a cog, fitting into a groove on something else and turning it.
Here are some splines:
Where can you spot splines? On bicycles, food mixers, cassettes.
In fact any long narrow strip of wood or metal (or anything fairly rigid, really) can be a spline. You sometimes use them to connect two grooved tiles or boards together.
Spline is also an slightly old-fashioned term for those plastic bendable strips used to help people draw curves.
There are also multivariate adaptive regression splines, or MARS. They're something to do with statistical modelling.
They're terribly useful and interesting, probably, but they make me very glad I'm a novelist, and have to deal with nothing much more complicated at the moment than the Georgian Criminal Legal System.
Or putting the food mixture together.
Spot the Frippet: spline. This word appeared in the 1700s. It comes from an East Anglian dialect word, perhaps related to the word splint, which comes from the Old High German spaltan, to split.