idea vs topic

idea

noun
  • A musical theme or melodic subject. 

  • An abstract archetype of a given thing, compared to which real-life examples are seen as imperfect approximations; pure essence, as opposed to actual examples. 

  • A conception in the mind of something to be done; a plan for doing something, an intention. 

  • A purposeful aim or goal; intent 

  • More generally, any result of mental activity; a thought, a notion; a way of thinking. 

  • An image of an object that is formed in the mind or recalled by the memory. 

  • A vague or fanciful notion; a feeling or hunch; an impression. 

topic

noun
  • Subject; theme; a category or general area of interest. 

  • Discussion thread. 

  • A musical sign intended to suggest a particular style or genre. 

adj
  • topical 

How often have the words idea and topic occurred in a corpus of books? (source: Google Ngram Viewer )