What is the meaning of idea?

noun

• The content of cognition; the main thing you are thinking about.
  • usage: "it was not a good idea"; "the thought never entered my mind"
  • synonyms: thought
• Your intention; what you intend to do.
  • usage: "he had in mind to see his old teacher"; "the idea of the game is to capture all the pieces"
  • synonyms: mind
• A personal view.
  • usage: "he has an idea that we don't like him"
• An approximate calculation of quantity or degree or worth.
  • usage: "an estimate of what it would cost"; "a rough idea how long it would take"
  • synonyms: estimate, estimation, approximation
• Music) melodic subject of a musical composition. (
  • usage: "the theme is announced in the first measures"; "the accompanist picked up the idea and elaborated it"
  • synonyms: theme, melodic theme, musical theme