1. a person or thing that is mysterious, puzzling, or difficult to understand
2. a riddle or puzzling question, especially one expressed in metaphorical language

Examples

• The disappearance of the ancient civilization remains an enigma to archaeologists.
• Her sudden change in behavior was an enigma to her friends.
• The professor posed an enigma that challenged even his brightest students.
• The artist’s true identity became an enigma that fascinated the public.
• Scientists are still trying to solve the enigma of dark matter.
• The old mansion held many enigmas within its walls.