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

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

From BBC

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.

From Los Angeles Times

In 2020 your sister published “Open Book,” which is one of the frankest celebrity memoirs I’ve read.

From Los Angeles Times

He's noticed a marked improvement this year, where at university some of his exams have been open book, which he says he has preferred to his assessments at school.

From BBC

Despite this bout of caution, Einbinder can also be an open book.

From Los Angeles Times