nefarious

Etymology

From Latin nefārius (“execrable, abominable”), from nefās (“something contrary to divine law, an impious deed, sin, crime”), from ne- (“not”) + fās (“the dictates of religion, divine law”), which is related to Latin for (“I speak, I say”) and cognate to Ancient Greek φημί (phēmí, “I say”).

adj

1. Sinful, villainous, criminal, or wicked, especially when noteworthy or notorious for such characteristics.
   Aliens have a nefarious connotation in many science fiction books.
   "If the vessel be no fair-trading slaver, nor a common cruiser of his Majesty, it is as tangible as the best man's reasoning, that she may be neither more nor less than the ship of that nefarious pirate the Red Rover." 1828, James Fenimore Cooper, chapter 2, in The Red Rover
   Mommsen […]declares that Catiline in particular was "one of the most nefarious men in that nefarious age. His villanies belong to the criminal records, not to history." 1877, Anthony Trollope, chapter 9, in The Life of Cicero
   The fact that the room was still in darkness made it obvious that something nefarious was afoot. Plainly there was dirty work in preparation at the cross-roads. 1921, P. G. Wodehouse, chapter 26, in The Indiscretions of Archie
   I try to let everyone back here in Minnesota know exactly the nefarious activities that are taking place in Washington. 2009 October 14, Monica Davey, “Fact Checker Finds Falsehoods in Remarks”, in New York Times, retrieved 2014-05-12