closed book

noun

1. something that is not known or cannot be understood; a mystery or puzzle:

   Abstract art is a closed book as far as I'm concerned.

closed book

noun

1. something deemed unknown or incapable of being understood
2. a matter that has been finally concluded and admits of no further consideration

Word History and Origins

Origin of closed book¹

First recorded in 1910–15

Example Sentences

Mr Ba may have been on the political scene for the last decade, but he is a bit of a closed book for most.

From BBC

“As you know, I’m not normally a closed book on this stuff,” Sean told me.

From Washington Post

When the bank collapsed, her loan was one of thousands sold by the government to so-called "closed book" lenders.

From BBC

The answer was always there, tucked away within the brittle pages of that closed book—Papá.

From Literature

A "free hit" is how Mott described the je ne sais quoi that Stokes brings to the team, with his inclusion in England's XI a closed book as far as Foster is concerned.

From BBC

Related Words

• conundrum
• enigma
• problem
• question
• riddle
• secrecy
• subtlety
• thriller