Advanced as in riddle A mystery or enigma, similar to a riddle, that is difficult or impossible to understand or decipher. Clear All
2 Example Sentences Showcasing the Meaning of 'Closed Book'
Despite countless attempts, the alien technology was a closed book to Earth scientists, leaving them puzzled and intrigued.
The encrypted message proved to be a closed book for the codebreakers, requiring exceptional skills to decipher its meaning.
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