an open book
Meaning
Someone whose thoughts, feelings, or life are easy to understand because they hide nothing.
Origin
A metaphor from a book lying open: anyone can read what’s inside, so an “open book” person is easy to “read” and not secretive. Recorded in English from the 19th century.
Notes
Usually positive (honest, transparent), but can be cautionary in business/negotiations: being too readable or revealing too much.
Examples
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Ask me anything—I'm an open book.
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With her parents, he's an open book about his career plans.
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I'm not an open book at work, but my close friends know everything.
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The manager is an open book, so you always know where you stand.
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His face is an open book; you can tell when he's worried.
Grammar & Usage Notes
Typically used as a noun phrase with the article: “be an open book (to someone).” Can be modified (e.g., “pretty much an open book”). Less common as “like an open book” in similes.
Synonyms
- transparent
- easy to read
- an open person
- wear one’s heart on one’s sleeve
Antonyms
- closed book
- mystery
- hard to read
- guarded
- secretive