idea: [16] Etymologically, an idea is the ‘look’ of something – it comes ultimately from the same source as produced the Greek verb ídein ‘see’. Greek idéā itself was used by Plato in the specialized sense ‘archetypal form of something’, which survives in the derived adjective ideal [17], but as far as the modern English noun is concerned, its sense ‘notion, mental conception’ developed (in Greek) via ‘look, appearance’, ‘image’, and ‘mental image’. Ideology [18] is a derivative, coined originally in French at the end of the 18th century. => ideology, idol
idea (n.)
late 14c., "archetype of a thing in the mind of God; Platonic `idea,'" from Latin idea "idea," and in Platonic philosophy "archetype," from Greek idea "ideal prototype," literally "the look of a thing (as opposed to the reality); form; kind, sort, nature," from idein "to see," from PIE *wid-es-ya-, suffixed form of root *weid- "to see" (see vision). Sense of "result of thinking" first recorded 1640s.
Men of one idea, like a hen with one chicken, and that a duckling. [Thoreau, "Walden"]
Idée fixe (1836) is from French, literally "fixed idea."
例文
1. I have a fair idea of how difficult things can be.
状況がどのくらい難しいか大体知っています。
2.They have only a vague idea of the amount of water available.
彼らは水の総量を知っているだけだ。
3.Professor Baker is unacquainted with the idea of representative democracy.
ベイカー教授は「代議制民主」という思想に精通していない。
4.The police told me.It was a bombshell.I had no idea .
は警察に教えてもらった。驚きました、全く思いませんでした。
5."I told you Preskel had no idea ，"remarked Kemp with some asperity.