/ Dictionary / Index O open book: Meaning and Definition of Find definitions for: o'pen book' Pronunciation: [key] someone or something easily understood or interpreted; something very clear: The child's face is an open book. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. open bar open call Related Content Daily Word Quiz: arid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language