The definition of nefarious is someone who is known for being very wicked.
An example of nefarious is Adolf Hitler.
very wicked; villainous; iniquitous
Origin of nefariousClassical Latin nefarius from nefas, crime, sin from ne-, not + fas, (divine) law, lawful
Infamous by way of being extremely wicked.
Origin of nefariousLatin nefārius from nefās crime, transgression ne- not ; see ne in Indo-European roots. fās divine law ; see dhē- in Indo-European roots.
(comparative more nefarious, superlative most nefarious)