English version

a closed book (to somebody)

From Longman Dictionary of Contemporary Englisha closed book (to somebody)a closed book (to somebody)NOT KNOWa subject or problem that someone does not know about or understand 🔊 Mathematics has always been a closed book to me. closed
Examples from the Corpus
a closed book (to somebody)I can not believe that it can be right that this late in the game Poetry is still a closed book.The kitchenette is a closed book.The Shoah will never be a closed book.I tell myself it's a closed book, but my cover story becomes an old man's compensation.But your own past can be a closed book, even at fourteen.He is holding a closed book, signifying a mystery, possibly a stage in the alchemical process.The highly organised St Stephen's Society programme which she now leads was at that time a closed book to her!Linear preoccupation in the past remains a closed book to modern understanding.
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