# closed book

idiom

Source: https://englishreference.com/idiom/closed-book
Updated: 2026-08-10

## Meaning

A person or thing that cannot be easily understood; someone or something incomprehensible or puzzling.

## Examples

- He is a closed book to me.
- I have worked with him for years, but he remains a closed book regarding his personal life.
- Despite her outward friendliness, she remained a closed book, leaving her colleagues to wonder about the true motivations behind her sudden resignation.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.