The Greek goddess of the rainbow and a messenger of the gods.

Rainbow.

ETYM Latin iris, iridis, the goddess, Greek iris, the rainbow, iris of the eye, the plant Iris. Related to Orris.
Plants with sword-shaped leaves and erect stalks bearing bright-colored flowers composed of three petals and three drooping sepals; SYN. flag, fleur-de-lis, sword lily.
In botany, perennial northern temperate flowering plants of the genus Iris, family Iridaceae. The leaves are usually sword-shaped; the purple, white, or yellow flowers have three upright inner petals and three outward-and downward-curving sepals. The wild yellow iris is called flag.

In anatomy, the colored muscular diaphragm that controls the size of the pupil in the vertebrate eye. It contains radial muscle that increases the pupil diameter and circular muscle that constricts the pupil diameter. Both types of muscle respond involuntarily to light intensity.
Muscular diaphragm that controls the size of the pupil; it forms the colored portion of the eye.
Thin overlapping plates can be adjusted to change the diameter of a central opening; SYN. iris diaphragm.