1. the quality of being extremely cruel, wicked, or evil
2. the quality of being extremely difficult or challenging
Usage: informal

Examples

• The fiendishness of the villain’s plan shocked everyone.
• She was appalled by the fiendishness of the crime.
• The puzzle’s fiendishness made it nearly impossible to solve.
• His fiendishness in business dealings earned him many enemies.
• The fiendishness of the math problem frustrated the students.
• The novel explored the fiendishness of human nature.
• The fiendishness of the trap caught even experienced hunters off guard.