fiendish
(Informal)
[adjective]
Synonyms: wicked, cruel, devilish, diabolical, hellish, infernal, malignant, monstrous, satanic, unspeakable

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Contrasted words: benign, benignant, kind, kindly, gentle, mild, compassionate, sympathetic, tender
Related Words: hellish, infernal, baleful, malefic, maleficent, malign, sinister, malevolent, malicious, malignant, atrocious, heinous, monstrous, outrageous, barbarous, cruel, ferocious, inhuman, savage, vicious

[TahlilGaran] English Synonym Dictionary ▲

fiend‧ish /ˈfiːndɪʃ/ adjective

1. cruel and unpleasant:
a particularly fiendish practical joke

2. very clever in an unpleasant way:
a fiendish plan

3. extremely difficult or complicated:
several fiendish exam questions
—fiendishly adverb
—fiendishness noun [uncountable]

[TahlilGaran] Dictionary of Contemporary English ▲