SOLID IMPRESSION

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.