Nefarious
Extreme wickedness
Adjective:
Synonyms: vile, wicked, evil, sinful, monstrous
Antonyms: good, honest, hero, nice
Sentences:
The teacher showed she was nefarious when she gave her students hours of homework.
The robber was nefarious when he took a hostage and threatened to kill her.
The Y.K. Dictionary - Nefarious