be a closed book

be a closed book

To be difficult to know or understand. She's such a private person that I don't know much about her. I guess she's a closed book. I'm a scientist through and through, so art has always been a closed book to me.
See also: book, closed
Farlex Dictionary of Idioms.
See also:
  • a closed book
  • closed book, a
  • I know
  • Don’t I know it!
  • don't I know it
  • as we know it
  • before you know it
  • as you know
  • can't say as I do
  • (I) can't say as I do