open book
open book — noun
1. a person who makes no effort to conceal their inner thoughts or emotions, making
a person who makes no effort to conceal their inner thoughts or emotions, making it simple for other people to read their state of mind.
Nora is an open book — when she feels upset, her face shows it right away.
predicative: [person] is an open book
Jude has always been an open book, happily telling coworkers about his weekend plans.
always been an open book — adverb between copula and noun
Mei tried to hide her disappointment, but she is an open book and everyone guessed.
The witness was an open book on the stand, answering every question without any delay.
Imani never lies; she is an open book, and her friends value that honesty.
- transparent
less metaphorical; implies motives are visible rather than personality being readable
- guileless
more formal, emphasises lack of deceit rather than ease of reading
- frank
focuses on speech rather than overall demeanour
- closed book
the direct opposite idiom for someone whose thoughts are hard to read
- enigma
more formal; a person who is puzzling and hard to understand
文法句型
[person] is an open book
用法筆記
Frequently used with the verb be (is / was / has always been) in a predicative pattern — the person is described as an open book rather than having one. The phrase rarely appears with an article other than an, and almost never in the plural.
常見錯誤
open book — idiom
1. a situation, fact, or thing that is completely known or understood, with nothing
a situation, fact, or thing that is completely known or understood, with nothing hidden, secret, or mysterious about it.
After the new policy took effect, the company's spending became an open book to everyone.
became an open book — change-of-state verb with the idiom
Walid's family history is an open book; he shares old photos without any hesitation.
subject is abstract possession: [possessor]'s [thing] is an open book
For the experienced detective, the case was an open book from the very first day.
Minh posted the recipe online, so the method is now an open book for anyone.
Amelia keeps her research notes on a shared drive, making the project an open book.
- transparent
more general; can apply to systems, processes, or people
- unconcealed
more formal; emphasises that nothing is hidden
- plain to see
informal; similar meaning but adjectival rather than noun-based
- closed book
direct opposite for a thing that is not understood
- mystery
a thing that is not known or understood
文法句型
[thing] is an open book
用法筆記
Distinguish from the noun sense (EASY TO READ): the idiom sense describes a thing, fact, or situation rather than a person. Often used after verbs of disclosure such as become, make, or keep. Common in business and journalistic contexts about transparency.