open book

noun

1. someone or something easily understood or interpreted; something very clear.

   The child's face is an open book.

open book

noun

1. a person or thing without secrecy or concealment that can be easily known or interpreted

Word History and Origins

Origin of open book¹

First recorded in 1850–55

Idioms and Phrases

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.

Example Sentences

"Now I'm an open book...six years ago, I couldn't even say the words periods without flushing red," she added.

Read more on BBC

Some of Demoff's closest friends in the industry are at the San Francisco 49ers, who now own Leeds United and Rangers too, but "we're all competitors. There's only so much people are willing to share, whereas here, there is no limit. Everybody realises that being an open book makes us all better".

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Eilish has been “somewhat of an open book” as long as she can remember.

Read more on The Wall Street Journal

"We're a very open book in this family," she said.

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After re-signing with the Dodgers following MLB’s 2022 lockout, Kershaw reported to Dodgers camp as an “open book” to training staff, current major league strength coach Travis Smith recalled.

Read more on Los Angeles Times