English▸ noun [mass noun]
1 the unrealistic belief in or pursuit of perfection. Compare with realism:
the idealism of youth.
▪ (in art or literature) the representation of things in ideal or idealized form. Often contrasted with realism (sense 2 of the noun)
2 Philosophy any of various systems of thought in which the objects of knowledge are held to be in some way dependent on the activity of mind. Often contrasted with realism (sense 3 of the noun)
– ORIGIN mid 18th century (in idealism (sense 2 of the noun)): from ideal + -ism, after French idéalisme or German Idealismus.