Fiendish
Fiendish adjective - Of, relating to, or worthy of an evil spirit.
Usage example: a fiendish delight in playing cruel tricks
Sinister and fiendish are semantically related. In some cases you can use "Sinister" instead an adjective "Fiendish".
Nearby Words: fiend, fiendishly
Sinister
Sinister adjective - Being or showing a sign of evil or calamity to come.
Mutual synonyms
Both words in one sentence
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Given that her admirer is a ferocious werewolf who loves the sinister and fiendish, a human might find her to be a malevolent yet alluring temptress, or a stark reminder that other beings' preferences may be a tad different than our own.
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Jiminy Cricket: Avoid anybody with a fiendish cackle, sinister smile, or diabolical glare.
Source: Obviously Evil - Crab "has some weird, fiendish new weapon." But just as he is preparing for a possible fight to the death, the sinister sound is revealed as nothing more than a ghetto blaster pumping out hip-hop beats as it is carried by a Vanilla Ice-like teenager.
Cite this Source
Sinister and Fiendish. (2016). Retrieved 2026, August 01, from https://thesaurus.plus/related/fiendish/sinister
Fiendish & Sinister. N.p., 2016. Web. 01 Aug. 2026. <https://thesaurus.plus/related/fiendish/sinister>.
Sinister or Fiendish. 2016. Accessed August 01, 2026. https://thesaurus.plus/related/fiendish/sinister.
Google Ngram Viewer shows how "fiendish" and "sinister" have occurred on timeline