/ Dictionary / Index O open sight: Meaning and Definition of Find definitions for: o'pen sight' Pronunciation: [key] (on a firearm) a rear sight consisting of a notch across which the gunner aligns the front sight on the target. Cf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. open-sided open space Related Content Daily Word Quiz: reluctant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language