noun
fiend
FEEND/fiːnd/
A demon imagined as violently wicked.
The horned fiend crouches with bared fangs and reaching claws.

Etymology
Feond meant an enemy and came to name the Devil as humanity's adversary, then a diabolical person. The use for an obsessive devotee, as in “dope fiend,” is a later extension.
In context
He's an alcohol fiend just like me, dude. My homie is a drinker.
More examples
- In the legend, a fiend rises from the pit to attack travelers.
- The wizard summons a fiend that turns against him.
- The villagers pray for protection from the fiends roaming the forest.
Forms
fiend · fiends
fiendish adjective — Extremely wicked, cruel, or devilish.