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 nef&amacron;rius, from nef&amacron;s, crime, transgression : ne-, not; see ne in Indo-European roots + f&amacron;s, divine law; see dh&emacron;- in Indo-European roots.
(comparative more nefarious, superlative most nefarious)