as in mysteries
something hard to understand or explain the couple's unorthodox marriage is definitely a closed book to those outside of the relationship
Synonyms & Similar Words
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Example Sentences
Recent Examples of Synonyms for closed books
Noun
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The research also shows how quantum technologies are providing new tools to study the fundamental mysteries of physics.—
Ameya Paleja, Interesting Engineering, 20 Apr. 2026
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Our universe is full of mysteries, but few are as perplexing as the dark, tiny galaxies that hover around larger ones like the Milky Way.— Paul Sutter, Space.com, 20 Apr. 2026
Noun
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Check out the all new PLAY hub with puzzles, games and more!— Eve Chen, USA Today, 19 Apr. 2026
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To find her way out, Miskwa must solve puzzles and navigate different environments while learning Ojibwe words and phrases along the way.— Joe Van Ryn, CBS News, 15 Apr. 2026
Noun
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When secrets are a matter of national security Now consider how much worse that problem becomes if that AI helper works for the CIA, where secrecy is a matter of national security and breaches could endanger lives.— Erik German, Fortune, 11 Apr. 2026
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Its secrets have been passed down through four generations.— Bill Addison, Los Angeles Times, 11 Apr. 2026
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“Closed books.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.grautoblog.com/thesaurus/closed%20books. Accessed 23 Apr. 2026.
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