/ Dictionary / Index O optic chiasma: Meaning and Definition of Find definitions for: op'tic chias'ma Pronunciation: [key] a site at the base of the forebrain where the inner half of the fibers of the left and right optic nerves cross to the opposite side of the brain. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. optic center optician Related Content Daily Word Quiz: impetuous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language