notion

/ˈnoʊʃən/
noun
  1. An idea, belief, or opinion about something.
    • He rejected the notion that hard work alone guarantees success.
    • The notion that money brings happiness is not always true.
    • She had a vague notion that the answer was in the book.
  2. A sudden desire or impulse to do something.
    • I had a notion to go for a walk in the rain.
    • On a whim, she took a notion to paint her room bright yellow.
    • He got a notion to learn the guitar overnight.