■ noun
1》 a flat, coloured, ring-shaped membrane behind the cornea of the eye, with an adjustable circular opening (pupil) in the centre.
2》 a plant with showy flowers, typically purple or yellow, and sword-shaped leaves. [Genus Iris : many species.]
3》 (also ~ diaphragm ) an adjustable diaphragm of thin overlapping plates for regulating the size of a central aperture.
■ verb open or close in the manner of an ~.
Origin
mod. L., via L. from Gk ~ 'rainbow, ~'.