Eidos comes from Ancient Greek εἶδος (eîdos, "form, shape, essence"), from the Proto-Indo-European root *weid- ("to see"); adopted into English as a philosophical term for ideal form or essence. In current use it is a noun meaning "the ideal form or essence of something, especially in philosophical contexts". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.