Today we use is to talk of transcendent entities, a standard of perfection, a plan of action. It could also mean representation of a concept. An image recalled by memory, an indefinite or unformed conception. An entity actually potentially present to consciousness or just a formulated thought or opinion, sometimes it is the central meaning or chief end of a particular action or situation. Whatever is known or supposed about something like a child’s idea of time is another popular use.
If i were to talk about my idea of a surreal experience, it would my idea of a marked irrational reality of dream. Not really difficult,
Not very easy either, what would really be surreal? May be the dream where my grandparents are driving down in a car en route they pick up an elderly relative when we reach the river bank instead of driving through the bridge my grandma tells me to get off the car and drive down with mom. The three of them drive through Gran says it’s because they have to move on, next morning I hear that particular relative has passed away. My grandparents have been dead for 15yrs now.