The colored part of the eye that controls how much light enters the pupil; also plural of iris, a flowering plant with sword-shaped leaves.
From Greek 'iris,' meaning 'rainbow,' because of the varied colors found in eye irises and the flower. The flower was named for the goddess Iris, who represented the rainbow in Greek mythology.
The iris flower and the iris of your eye are the same word because ancient Greeks saw both as rainbows—the flower has colorful petals and your eye's iris is the colorful part—showing how poetic the ancients were when naming things!
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