English

Noun

closed book ‎(plural closed books)

1. (idiomatic) A 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!" — Prisoners by Mary Cholmondeley

Antonyms

• open book

See also

• enigma
• mystery
• secret