1.nounThe property of a person of having high ideals that are usually unrealizable or at odds with practical life.
2.nounThe practice or habit of giving or attributing ideal form or character to things; treatment of things in art or literature according to ideal standards or patterns;—opposed to realism.
3.nounAn approach to philosophical enquiry, which asserts that direct and immediate knowledge can only be had of ideas or mental pictures.