What does "fiendishly" mean?

In a fiendish manner; evilly, wickedly.

What is a synonym for "fiendishly"?

Common synonyms include: diabolically, atrociously, cruelly, devilishly, devilishly, devilishly.

//ˈfiːndɪʃli// adv

adv ·Uncommon ·Advanced level

Adverb

1
In a fiendish manner; evilly, wickedly.
"At a side door, reclined on a couch, two guards of the haram, with their naked swords grasped in their hands, and features, fiendishly contorted between sleep and dissolution, seemed to menace death to any who should venture to approach."
2
Extremely, very in harsh or negative contexts.
"Either the Russians are so fiendishly clever that they've managed to keep one of their agents running in this organization for over twenty years or they're so fiendishly clever that they're sending us false defectors to claim that they have."

Adverb

"His long, claw-like fingers danced from one part of the machine to another fiendishly, and a hideous grin distorted his features."

From fiendish + -ly.

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.