/ Dictionary / Index A aperture: Meaning and Definition of Find definitions for: ap•er•ture Pronunciation: (ap'ur-chur), [key] — n. an opening, as a hole, slit, crack, gap, etc. Also calledan opening, usually circular, that limits the quantity of light that can enter an optical instrument. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: aperture (Thesaurus) apertometer aperture mask Related Content Daily Word Quiz: morose Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language