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late 14c., flowering plant (Iris germanica), also "prismatic rock crystal," from Latin iris (plural irides) "iris of the eye, iris plant, rainbow," from Greek iris (genitive iridos) "a rainbow; the lily; iris of the eye," originally "messenger of the gods," personified as the rainbow. The eye region was so called (early 15c. in English) for being the colored part; the Greek word was used of any brightly colored circle, "as that round the eyes of a peacock's tail" [Liddell and Scott].
iris i·ris (ī'rĭs)
n. pl. i·ris·es or i·ri·des (ī'rĭ-dēz', ĭr'ĭ-)
The round pigmented contractile membrane of the eye that is perforated in the center by the pupil, forms the front part of the vascular tunic, and is attached on the margin to the ciliary body.
Institute for Research in Information and Scholarship of Brown University (Providence RI).
in Greek mythology, the personification of the rainbow and (in Homer's Iliad, for example) a messenger of the gods. According to the Greek poet Hesiod, she was the daughter of Thaumas and the ocean nymph Electra. In Hesiod's works, at least, she had the additional duty of carrying water from the River Styx in a ewer whenever the gods had to take a solemn oath. The water would render unconscious for one year any god or goddess who lied. In art, Iris was normally portrayed with wings, and her attributes were the herald's staff and a vase. She was shown serving wine to the gods or escorting them to the wedding of Peleus and Thetis.
in anatomy, the pigmented muscular curtain near the front of the eye, between the cornea and the lens, that is perforated by an opening called the pupil. The iris is located in front of the lens and ciliary body and behind the cornea. It is bathed in front and behind by a fluid known as the aqueous humour. The iris consists of two sheets of smooth muscle with contrary actions: dilation (expansion) and contraction (constriction). These muscles control the size of the pupil and thus determine how much light reaches the sensory tissue of the retina. The sphincter muscle of the iris is a circular muscle that constricts the pupil in bright light, whereas the dilator muscle of the iris expands the opening when it contracts. The amount of pigment contained in the iris determines eye colour. When there is very little pigment, the eye appears blue. With increased pigment, the shade becomes deep brown to black. Inflammation of the iris is termed iritis or anterior uveitis, a condition that commonly has no determinable cause. As a result of inflammation, the iris sticks to the lens or the cornea, blocking the normal flow of fluid in the eye. Complications of iritis include secondary glaucoma and blindness; treatment usually involves topical steroid eyedrops.