n. 1 the flat circular coloured membrane behind the cornea of the eye, with a circular opening (pupil) in the centre. 2 any herbaceous plant of the genus Iris, usu. with tuberous roots, sword-shaped leaves, and showy flowers. 3 (in full iris diaphragm) an adjustable diaphragm of thin overlapping plates for regulating the size of a central hole esp. for the admission of light to a lens.
[ ME f. L iris iridis f. Gk iris iridos rainbow, iris ]