something deemed unknown or incapable of being understood
2.
a matter that has been finally concluded and admits of no further consideration
sealed book in American English
noun
something beyond understanding and therefore unknown
Word origin
[1810–20]This word is first recorded in the period 1810–20. Other words that entered Englishat around the same time include: dominance, duplex, keyboard, unitary, voodoo
Examples of 'sealed book' in a sentence
sealed book
But music upon the practical side remained a sealed book.
W. S. B. Mathews A Popular History of the Art of Music From the Earliest Times Until the Present (1891). Retrieved in 2019 from Project Gutenberg (https://www.gutenberg.org/ebooks/)