Iris

1. A plant of the genus Iris, common in the northern hemisphere, and generally having attractive blooms (See Iris (plant)).
2. The contractile membrane perforated by the pupil, which adjusts to control the amount of light reaching the retina, and which forms the colored portion of the eye (See Iris (anatomy)).
3. A diaphragm used to regulate the size of a hole, especially as a way of controlling the amount of light reaching a lens.
4. A rainbow, or other colourful refraction of light.
5. A constricted opening in the path inside a waveguide, used to form a resonator.
6. The inner circle of an oscillated color spot.

verb

(of an aperture, lens or door) To open or close in the manner of an iris.