Synonyms for Closed book

Synonyms starting with letter C

• conundrum

  brain-teaser, mystery, puzzle
• crux

  mystery, puzzle
• complexity

  brain-teaser
• cliffhanger

  mystery, puzzle
• cryptogram

  brain-teaser, mystery, puzzle
• charade

  puzzle, brain-teaser, mystery
• chiller
• complication

  brain-teaser
• confusion
• challenge
• confidential information
• case