open book

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open book (plural open books)

1. (idiomatic) Something of which salient aspects are obvious or easily interpreted.
   • 1860, Abby Maria Hemenway, “The Priest and The Maiden”, in Poets and Poetry of Vermont:

     There is one, with a dark and thoughtful eye,
     Who is to all others a mystery;
     But his soul is to me an open book,
     And I read his mood in his slightest look; ...

   • 1898, John Wesley Powell, Truth and Error or the Science of Intellection:

     This is the secret of Hegel, and the key to his hieroglyphics, and, if consistently used to interpret the sayings of his logic, it becomes an open book.

   • 1921, Edgar Rice Burroughs, Tarzan the Untamed:

     On the surface of the ground or through the swaying branches of the trees the spoor of man or beast was an open book to the ape-man, but even his acute senses were baffled by the spoorless trail of the airship.

   • 2009, May 21, Barack Obama, speech, Protecting Our Security and Our Values

     But I have never argued – and never will – that our most sensitive national security matters should be an open book.

2. (idiomatic) A person who through naivete responds candidly to questions or openly displays their emotions or intentions.
   • 1986, Adrienne von Speyr, Hans Urs von Balthasar, The Christian State of Life:

     He is an open book. Everyone can see that he removes nothing, conceals nothing, reserves nothing for himself.

   • 1997, Matthew J. DeLuca, Best Answers to the 201 Most Frequently Asked Interview Questions:

     Chapter 3: Are You an Open Book? How Much Do I Need to Disclose?

   • 2002, Linda Lange, Feminist Interpretations of Jean-Jacques Rousseau:

     Emile's most striking characteristic is that he hides nothing. He is an open book, acting the same in private as in public — "Emile is worse at disguising his feelings than any man in the world."

3. (mathematics, topology) An open book decomposition.
4. (climbing) An inside angle in the rock.

• (person who is candid): one who wears one's heart on one's sleeve

• (antonym(s) of “person who is candid”): closed book

• open-book contract

• en clair
• open publication: open access book (e.g., open-access monograph)
• open secret
• wear one's heart on one's sleeve

• open book on Wikipedia.Wikipedia