An implacable or malicious foe; one who is diabolically wicked or cruel; an infernal being; -- applied specifically to the devil or a demon.

a cruel wicked and inhuman person

one of the evil spirits of traditional Jewish and Christian belief

a demon or an evil spirit

In the Dungeons & Dragons fantasy role-playing game, the player characters (fictional characters controlled by the players) often come into conflict with a variety of monsters from folklore and mythology. One of the game's more prominent monsters are the various races of demons, devils and other malicious otherworldly creatures, collectively referred to as fiends. These creatures are of wholly evil alignment and hail from the Lower Planes.