fiendish

Fiendish is an English adjective used to describe something that resembles a fiend or demon, or that is exceptionally wicked or cruel. It can also convey a sense of malicious cunning, as in a fiendish plan or fiendish scheme. In contemporary usage, the word frequently appears with a meaning of extreme difficulty or intricacy, such as a fiendish puzzle or a fiendishly difficult task.

Etymology: The term derives from the noun fiend, from Old English fiend meaning an enemy or demon. The suffix -ish forms adjectives meaning “having the qualities of” or “characteristic of.” The sense of malevolent intelligence or extreme difficulty developed in Early Modern English and is now common in both formal and informal registers.

Usage: In literature, film, and video games, fiendish is used to describe villains, traps, schemes, or challenges that feel deliberate, cruel, or exceptionally tricky. Phrases such as a fiendish smile or fiendishly clever solution are common. While overwhelmingly negative in tone, the word can be used playfully or hyperbolically without implying real harm.

See also: devilish, demonic, diabolical, wicked; fiend; fiendishness (noun).