When they first discovered that Australian curiosity of a mammal, scientists wanted platypus to be its genus name, but that was already taken up by a kind of boring beetle, so they kept platypus as a colloquial name and used ornithorhyncus for the genus name instead. Both the beetle and the mammal name mean "flat footed" and derive from the Ancient Greek word platupous, which itself is a portmanteau of platys, a word meaning "flat", and pous, a word meaning "foot". The former can be traced to the Proto-Indo-European root pele or pelh or plat or pleh (I have seen it in so many variations at this point, for it is quite a common root), all of which also meant "flat", and pous is a formation from ped, "foot", itself deriving from the Proto-Indo-European root pod, which also meant "foot". So, even if we haven't seen much semantic change, we at least now known that platypodes can't serve in the army. Oh, yeah, platypodes, not platypuses, or, God forbid, platypi.
Adam Aleksic has been described as the internet's sixth most famous etymologist. He loves writing about himself in the third person, he's a freshman at Harvard University, and he has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law.
The Etymology Nerd