/ Dictionary / Index I iris diaphragm: Meaning and Definition of Find definitions for: i'ris di"aphragm Pronunciation: [key] — Optics, Photog. Optics,Photog. a composite diaphragm with a central aperture readily adjustable for size, used to regulate the amount of light admitted to a lens or optical system. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. irisation iris diaphragm shutter Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language