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
Matter and closed book are semantically related. In some cases you can use "Matter" instead a noun phrase "Closed book".
Matter
Matter noun - A major object of interest or concern (as in a discussion or artistic composition).
Closed book and matter are semantically related. Sometimes you can use "Closed book" instead a noun "Matter".
Mutual synonyms
Cite this Source
Matter and Closed book. (2016). Retrieved 2026, August 14, from https://thesaurus.plus/related/closed_book/matter
Closed book & Matter. N.p., 2016. Web. 14 Aug. 2026. <https://thesaurus.plus/related/closed_book/matter>.
Matter or Closed book. 2016. Accessed August 14, 2026. https://thesaurus.plus/related/closed_book/matter.
Google Ngram Viewer shows how "closed book" and "matter" have occurred on timeline