Synonyms idea 
( (a thought, opinion or plan in your mind): I have to talk to John – he’s always full of good ideas.
thought (a word, idea, or image that you have in your mind): Let me have your thoughts on that report by Monday.
concept (a general idea or understanding of something): It is very difficult to define the concept of beauty.
notion a mental image or general idea: We have different notions of right and wrong.
image a mental picture of something: 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.