idea (a thought or plan in your mind): I have to talk to John; he’s always full of good ideas.
thought (something that you think of or remember): The thought of closing the window never crossed my mind.
concept (a general idea or understanding of something): She was unfamiliar with the basic concepts of geology.
notion (an idea or understanding of something): We have different notions of right and wrong.
image (a mental picture of something, or an idea of how someone or something is): I can’t get the image of the accident out of my mind.
prospect (a mental picture of a future event): Living in Michigan for a year was an exciting prospect.
impression (an idea or belief that is usually not certain): My first impression of him was favorable.