The word stereotype was borrowed in 1798 from a French word spelled the same way and with the same definition- but it's not the definition you think. At the time, stereotype referred to a type of metal plate cast from a mold that was used to print things, instead of using individual letters like was customary before that. This process would create identical or near-identical copies of pages that were then assembled into books or newspapers. However, a metaphorical shift soon took place, and by 1850, the word stereotype was applied to any kind of situation where a set of ideas is repeated, metonymically bringing us from the printing press to the archetypes inside the books themselves. Stereo- is from Ancient Greek stereos, meaning "solid" (this in turn is from Proto-Indo-European ster, meaning "stiff") and type traces to typos, meaning "impression" (reconstructed as deriving from PIE tew). So a stereotype is a "solid impression", which brings to mind the process of printing in general.
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.