fiend

Short definition from Wiktionary

Noun

1. 1
   A devil or demon; a malignant or diabolical being; an evil spirit.
2. 2
   A very evil person.
3. 3
   An enemy; a foe.
4. 4
   The enemy of mankind, specifically, the Devil; Satan.
5. 5
   An addict or fanatic.

Verb

1. 1
   To yearn; to be desperate.