adjective
extremely cruel or devilish; diabolical
-
The detective was baffled by the fiendish plot devised by the criminal mastermind.
-
That escape room had some seriously fiendish puzzles that had us stumped for hours.
-
I can't believe you beat that fiendish level in the game, you're a pro!
-
Her smile was fiendish as she plotted her revenge against her ex-boyfriend.