What do caterpillars have to do with either cats or pillars? Turns out, nothing with the latter but a lot with the former. The word was borrowed in the sixteenth century as catyrpel (alternatively catirpel or catirpeller) from the Old French word caterpilose, which meant "hairy cat". This was sort of along the lines of how we call that specific kind of caterpillar a "woolly mammoth". They really can look like fluffy animals. This term was loaned directly from Latin catta pilosa, with the same definition. Catta, though Proto-Germanic kattuz, which is surprisingly of Afro-Asiatic origin (but, in retrospect, that makes sense as the first cats were domesticated in Egypt). Pilosa, meaning "hairy", is a conjugation of pilus, "hair", and that comes from the Proto-Indo-European pil, which referred to one strand of hair. The word caterpillar peaked in usage in the 1860s and has since remained relatively constant in our language.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd