Closed book
Closed book noun - Something hard to understand or explain.
Usage example: the couple's unorthodox marriage is definitely a closed book to those outside of the relationship
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Synonyms for Closed book
Trouble and closed book are semantically related. In some cases you can use "Trouble" instead a noun phrase "Closed book".
Trouble
Trouble noun - An abnormal state that disrupts a plant's or animal's normal bodily functioning.
Closed book and trouble are semantically related. Sometimes you can use "Closed book" instead a noun "Trouble".
Mutual synonyms
Cite this Source
Trouble and Closed book. (2016). Retrieved 2026, August 13, from https://thesaurus.plus/related/closed_book/trouble
Closed book & Trouble. N.p., 2016. Web. 13 Aug. 2026. <https://thesaurus.plus/related/closed_book/trouble>.
Trouble or Closed book. 2016. Accessed August 13, 2026. https://thesaurus.plus/related/closed_book/trouble.
Google Ngram Viewer shows how "closed book" and "trouble" have occurred on timeline