Meanings
plural closed books
- idiomaticA person or thing that cannot be easily understood; someone or something incomprehensible or puzzling.
Her courteous, sedate, inexorable husband, whose will she could not bend, whom she could not cajole, whose mind was a closed book to her — a book which had lain by her hand for three years, which she had never had the curiosity to open!
1906, Mary Cholmondeley, Prisoners: Fast Bound in Misery and Iron1 more example
Like the activities of British Railways Research Department, developing, testing and modifying diesel locomotives before their acceptance for service is another behind-the-scenes activity which is a closed book to most passengers and to many railwaymen.
1962 April, R. K. Evans, “The Acceptance Testing of Diesel Locomotives”, in Modern Railways, page 266
Synonyms & antonyms
nounsomething that baffles understanding and cannot be explained
Synonym sets from Open English WordNet, CC BY 4.0.
Cite this entry
closed book. (n.d.). In WatkinsX Dictionary. Retrieved November 4, 2026, from https://dictionary.watkinsx.com/word/closed%20book
“closed book.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/closed%20book. Accessed November 4, 2026.
WatkinsX Dictionary, s.v. “closed book,” accessed November 4, 2026, https://dictionary.watkinsx.com/word/closed%20book.
Source: closed book on Wiktionary, CC BY-SA 4.0.