The guillotine was named for French physician Joseph-Ignace Guillotin, who (contrary to popular belief) did not invent the machine, but helped popularize it during the Reign of Terror. Before then, it was called the louisette, after its actual inventor, surgeon Antoine Louis. Now that that's established, Guillotin's name is a diminutive of Guillot, which is a different form of the surname Guillaume. That's a cognate of William and Wilhelm, which are from Proto-Germanic roots wiljo, meaning "desire", and helmaz, meaning "helmet". The former derives from Proto-Indo-European welh, which could mean "choose" or "want", and the latter traces to Proto-Indo-European kel, "to protect". Unsurprisingly, literary usage of the word guillotine peaked in the late 1790s and has been trending downward since.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.