Definition of "Iris" :

noun: diaphragm consisting of thin overlapping plates that can be adjusted to change the diameter of a central opening

noun: muscular diaphragm that controls the size of the pupil which in turn controls the amount of light that enters the eye; it forms the colored portion of the eye

noun: plants with sword-shaped leaves and erect stalks bearing bright-colored flowers composed of three petals and three drooping sepals