noun (n)

• the content of cognition; the main thing you are thinking about(noun.cognition)

  Example:
  It was not a good idea.
  

  Synonym:
  thought
  

  source: wordnet30
• your intention; what you intend to do(noun.cognition)

  Example:
  The idea of the game is to capture all the pieces.
  

  Synonym:
  mind
  

  source: wordnet30
• a personal view(noun.cognition)

  Example:
  He has an idea that we don't like him.
  

  source: wordnet30
• an approximate calculation of quantity or degree or worth(noun.cognition)

  Example:
  A rough idea how long it would take.
  

  Synonym:
  approximation, estimate, estimation
  

  source: wordnet30
• (music) melodic subject of a musical composition(noun.communication)

  Example:
  The accompanist picked up the idea and elaborated it.
  

  Synonym:
  melodic theme, musical theme, theme
  

  source: wordnet30
• The transcript, image, or picture of a visible object, that is formed by the mind; also, a similar image of any object whatever, whether sensible or spiritual.(noun)

  source: webster1913