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Synonyms

closed book

American  

noun

  1. something that is not known or cannot be understood; a mystery or puzzle.

    Abstract art is a closed book as far as I'm concerned.
closed book British  

noun

  1. something deemed unknown or incapable of being understood

  2. a matter that has been finally concluded and admits of no further consideration

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of closed book

First recorded in 1910–15

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Mr Ba may have been on the political scene for the last decade, but he is a bit of a closed book for most.

From BBC • Mar. 22, 2024

“As you know, I’m not normally a closed book on this stuff,” Sean told me.

From Washington Post • Apr. 26, 2023

A lot of the stuff we know as fact turns out to be closed book fiction, a version of the truth steeped in the memory and settled now as a matter of certainty.

From The Guardian • Apr. 26, 2020

In a way, it was a good ending, in the fact that it wasn’t completely definitive or a closed book.

From Los Angeles Times • Apr. 15, 2020

He did want, however, to see the evidence from King’s before he considered the matter a closed book.

From "Double Helix" by James D. Watson

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.