[adjective]a fiendish (= very bad and cruel) gang/attackera fiendish (= clever and difficult, and possibly bad) plot/scheme/plan/policy(UK dated) I'm in a fiendish (= very great) hurry.(UK dated) We abandoned the scheme because of the fiendish (= very great) costs.
FIENDISH
Meaning of FIENDISH in English
Cambridge English vocab. Кембриджский английский словарь. 2012