nefarious

extremely wicked

Wicked in the extreme; abominable; iniquitous; atrociously villainous; execrable; detestably vile.

Latin nefas (profane)

“They do treat 'em nefarious down thah on the wholesale plantations.”

— Winston Churchill, Project Gutenberg Complete Works of Winston Churchill

In Helsinki's shadowy corners, Stellan planned his nefarious scheme: to replace all street signs with funny faces. Not wicked crimes, but his smirk at city ordinances was pure mischievous delight.

At dusk, Devika strolled along the Ringstrasse when she spotted a shadowy figure slipping a stolen necklace into an antique pocket watch. The man's hushed laughter echoed through the evening as he disappeared into the labyrinth of back alleys, his nefarious deed complete.

“Secretary of State Colin Powell's former chief of staff, Lawrence Wilkerson, said Diego Garcia was used by the CIA for "nefarious activities".”