1. Satan; the devil.
2. any evil spirit; demon.
3. a diabolically cruel or wicked person. Synonyms: monster, savage, brute, beast, devil.
4. a person or thing that causes mischief or annoyance.
5. Informal: a person who is extremely addicted to some pernicious habit.
Origin: before 900AD; Middle English feend, Old English fēond; cognate with German Feind, Old Norse fjandr, Gothic fijands foe, original present participle of fijan - to hate.