Also found in: Dictionary, Financial, Encyclopedia, Wikipedia.
Related to open book: Open Book Fracture
an open book
1. Something that is easy to understand or decipher. These legal contracts are anything but an open book.
2. One who acts (or purports to act) honestly, with no secrets. Ask me anything, I'm an open book. Adam says he's an open book, but I've seen him sneaking out of his house late at night.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
(like an) open book
Fig. [of someone or something] easy to understand. Jane's an open book. I always know what she is going to do next. The committee's intentions are an open book. They want to save money.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
Something or someone that can be readily examined or understood, as in His entire life is an open book. This metaphoric expression is often expanded to read someone like an open book, meaning "to discern someone's thoughts or feelings"; variations of this metaphor were used by Shakespeare: "Read o'er the volume of young Paris' face," ( Romeo and Juliet, 1:3) and "O, like a book of sport thou'lt read me o'er" ( Troilus and Cressida, 4:5). [Mid-1800s] For an antonym, see closed book.
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.