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3. an open book

an open book

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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.

See also: book, open

an open book

available for anyone to see or know about Your health secrets will be an open book to anyone who can do an online search.

See also: book, open