What's the informal term for the spikes on the end of a dinosaur's tail?
And the answer: the thagomizer.
A thagomizer is the cluster of spikes on the tail of the Stegosaurus. The term was coined in 1982 by cartoonist Gary Larson in his comic The Far Side, which suggests the spikes were named after a fictional caveman named Thag Simmons. After the comic ran, "thagomizer" was gradually adopted within scientific circles, and is still used today.
Studded with four long spikes, the tail of a Stegosaurus is no laughing matter. Yet, thanks to cartoonist Gary Larson, it miraculously is. The caveman for which it is named might indeed be fictional, but scientists liked the joke so much that the "thagomizer" is now essentially a codified term to refer to a Stegosaurus' tail spikes, appearing insofar as scientific journals and earning its own Wikipedia page under the new name.
Interestingly, bones of dinosaurs rarely get new names. A 2006 article in New Scientist explains that, for the most part, a humerus is a humerus, whether that be human, dino, chicken, or other. It's only on rare occasion that bones of animals evolve to be so distinct that they earn themselves a new name. Larson, who was also a biologist, was well-aware of this deficiency.
In 1993, "thagomizer" entered public usage in practice. At the annual meeting of the Society of Vertebrate Paleontology, paleontologist Ken Carpenter was presenting data pointing to a Stegosaurus' application of its tail as a weapon when he recalled Larson's Far Side cartoon. Naturally, as a joke which is too good to pass up, he referred to it as a thagomizer, and the name stuck. Before long, institutions left and right were labelling their Stegosaurus tails as such, including the Smithsonian Institution.