adjective

like or appropriate to a devil in evil and cruelty.

devilish tortures

wicked,evil,accursed,sinful,iniquitous,nefarious,vile,foul,abominable,unspeakable,loathsome,monstrous,atrocious,heinous,hideous,odious,horrible,horrifying,shocking,appalling,dreadful,awful,terrible,ghastly,abhorrent,despicable,damnable,villainous,shameful,depraved,perverted,ungodly,dark,black,black-hearted,immoral,amoral,vicious,cruel,savage,brutish,bestial,barbaric,barbarous,cacodemonic,egregious,flagitious,facinorous

adverb

very; extremely.

a devilish clever chap